1. Introduction

Addiction has a huge impact in healthcare systems worldwide. One out of nine hospitalizations in the United States of America are made by patients with substance use disorder (SUD). Unfortunately, numbers have been increasing in recent years. Furthermore, approximately 28% of all SUD patients die within fifteen years after seeking treatment, with a mean age under 50 years. There are many different substances with addictive potential, e.g., alcohol, cocaine, or heroin.

The course of SUD is strongly influenced by social environment and existing comorbidities—both somatic and psychiatric. ADHD is a common comorbidity in SUD patients with a more severe course of substance use. ADHD is characterized by a persistent pattern of age-inappropriate levels of inattention and/or hyperactivity/impulsivity that results in functional impairment at work, education, or hobbies and affects family life, social contacts, and self-confidence. Usually, ADHD symptoms become apparent in childhood. However, around 40–50% of this population continues to experience ADHD symptoms in adolescence and adulthood, while hyperactivity often diminishes and inattention stays more prevalent. Research has shown that ADHD has a prevalence of 2.5% in adults and 3.4% in childhood. Moreover, a meta-regression analysis showed that the geographical location and year of study were not associated with variability in ADHD prevalence estimates.

Patients with ADHD are more likely to develop SUDs at a younger age. Furthermore, a large population-based epidemiological study showed that ADHD symptoms were associated with significantly increased risks for alcohol use disorder, illicit drug use, and multiple substance use. However, the reason for the increased association between ADHD and SUD is unknown, although some authors suggest that substance use represents an attempt to self-medicate ADHD symptoms. Thus, therapeutic strategies of both disorders should be taken into consideration while treating young adults with SUD and ADHD. Psychopharmacological treatment alone does not appear to be particularly effective at treating SUD in currently active substance-using patients with ADHD. Multimodal therapies may be effective at treating patients with ADHD and comorbid SUD.

Current data indicate an ADHD prevalence of 21.5% in SUD populations. However, there were many attempts to estimate the prevalence of ADHD among SUD populations over the last decades, with inconsistent data ranging from 5.22% to 62%. Investigations of different SUD populations being addicted to different substances show that an increased prevalence of ADHD can be found in almost every SUD population. Both stimulant substances and sedative substances appear to be used by ADHD patients frequently. There are studies in populations of cocaine users showing ADHD prevalence between 14.5% and 20.5%. In populations of patients with alcohol addiction studies, there was an estimated ADHD prevalence between 7.7% and 62%, and among opioid users, an ADHD prevalence of 16.8% was shown. The most current meta-analysis we know of was published in 2012. Here, the estimated prevalence of ADHD among SUD populations was 23.1%. Furthermore, the meta-analysis showed that ADHD prevalence in adolescents was 25.3% and that ADHD prevalence in adults was 21.0%. However, up to this day, there is no screening for ADHD in daily clinical routine treatment of patients with SUD. We therefore decided to perform a new meta-analysis including the most recent studies in order to highlight the impact of ADHD in SUD more profoundly.

Objectives: The aim of this meta-analysis is to obtain an estimate of ADHD prevalence among adult SUD patients and SUD subpopulations for different substances, which could lead to a better understanding of the correlation between these two different psychiatric diseases, thus allowing the potential necessity of implementing screening tools for ADHD in SUD and vice versa to be studied.

2. Materials and Methods

2.1. Search Strategies

The structure of the meta-analysis was based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) 2020 guideline. Literature research of the PUBMED^® and Web of Science^® databases took place using the search terms [ADHD], [prevalence], and [substance use disorder]. The time period for inclusion was from 1970 to 2022. Reference lists of obtained articles were also considered. The search was conducted from 11 May 2022 to 7 July 2022.

2.2. Study Selection

The following inclusion criteria were used (1) a publication of the research paper in a peer-reviewed journal, (2) the formal diagnosis of SUD according to DSM or ICD, (3) the formal diagnosis of ADHD in adults or adolescents according to DSM or ICD (diagnosis based only on a self-report questionnaire is not sufficient), and (4) whether systematic and sufficient screening among SUD populations had been performed. The following exclusion criteria were used (1) publications only using secondary analysis of data (e.g., systematic reviews), (2) the paper not being eligible in English or German language, and (3) a lack of information necessary for the meta-analysis.

For an overview of study inclusion and exclusion, see Figure 1. We assessed the risk of bias based on seven domains and used risk-of-bias VISualization (robvis) to create risk-of-bias plots for the included studies.

Figure 1.

_{PRISMA 2020 flow diagram.}

2.3. Recorded Variables

The extracted variables from each study were sample size, gender distribution, the mean age of the participants, the prevalence of ADHD among the population, and the main substance of use. For the purpose of this meta-analysis, we only extracted subpopulations of opioid-, cocaine-, and alcohol users. Studies with other substances as the main substance or with missing information on a main substance were declared to be various types of substance use. If sub-populations were specified within a study, we tried to take them into account in the analysis. Data were extracted and checked from each study by one and the same researcher (N.G.).

2.4. Meta-Analytic Approach

The meta-analytic procedure was realized using R-software library package metafor [version 2.0-0]. A random-effects model was calculated based on logit transformation of single proportions to obtain overall proportion. Inverse variance weighting was chosen, and between-study variance was calculated using Der Simonian Laird estimator. Heterogeneities were assessed with Q and I² statistics. Conventions were followed by the interpretation of I²: values of 0.25, 0.50, and 0.75 correspond to low, moderate, and high between-trial heterogeneities. The publication bias was assessed with funnel plots and an egger intercept. Further, since age was not further specified as an inclusion criterion, meta-regression with age as a moderator variable was performed.

We conducted the same methods on the three SUD subpopulations: cocaine, opioids, and alcohol.

3. Results

3.1. Included Studies and Sample Characteristics

We screened 1691 records and included 31 studies with a total participant size of 12,524. Three studies with opioids (n = 2357), seven studies with cocaine (n = 2974), and seven studies with alcohol (n = 2143) as the main substance of use were included. For a list of included studies, see Table 1. The risk of bias of the included studies was estimated as overall low see Figure 2 and Figure 3.

Table 1. Included studies.

Figure 2.

_{Risk-of-bias traffic light plot of included studies.}

Figure 3.

_{Risk-of-bias summary plot of included studies.}

3.2. Meta-Analytic Findings

With a random-effects model, we determined the general ADHD prevalence among SUD patients of 21% (95% CI = [0.1741; 0.2548]). Significant heterogeneity was present (I² = 95.8%, Q = 721.09; df = 30; p < 0.0001). A moderator analysis was conducted for age, suggesting that age has only a slight influence on heterogeneity, Q (df = 25) = 20.2909, p = 0.7314. For the Forest plot of the effect sizes and 95% confidence intervals, see Figure 4. The visual inspection of the funnel plots and the egger intercept (z = −1.69, p = 0.30) suggest the absence of a publication bias (see Figure 5).

Figure 4.

_{Forest plot of the effect sizes and 95% confidence intervals for ADHD prevalence.}

Figure 5.

_{Assessment of publication bias with funnel plots for ADHD prevalence.}

While we were able to calculate the general prevalence of ADHD among SUD patients, there were unfortunately very few heterogenous data for the subpopulations for each substance on its own. Hence, the following data should be interpreted with caution.

For the subpopulation of cocaine users, we calculated an ADHD prevalence of 19% (95% CI = [0.1058; 0.3102]) with significant heterogeneity (I²= 96.7%, Q = 238.89; df = 8; p < 0.0001). For Forest and Funnel plots, see Figure 6.

Figure 6.

_{Forest plot of the effect sizes and 95% confidence intervals, and assessment of publication bias with funnel plots for the subpopulation of cocaine users.}

For the subpopulation of opioid users, we calculated ADHD prevalence of 18% (95% CI = [0.0784; 0.3505]) with significant heterogeneity (I²= 97.4%, Q = 153.26; df = 4; p < 0.0001). For Forest and Funnel plots, see Figure 7.

Figure 7.

_{Forest plot of the effect sizes and 95% confidence intervals, and assessment of publication bias with funnel plots for the subpopulation of opioid users.}

For the subpopulation of alcoholics, we calculated ADHD prevalence of 25% (95% CI = [0.1845; 0.3360]) with significant heterogeneity (I² = 92.5%, Q = 106.55; df = 8; p < 0.0001). For Forest and Funnel plots, see Figure 8.

Figure 8.

_{Forest plot of the effect sizes and 95% confidence intervals, and assessment of publication bias with funnel plots for the subpopulation of alcoholics.}

Unfortunately, we were not able to conduct the moderator analysis on these subpopulations because of the small n among them.

4. Discussion

Our main aim was to obtain an estimate of the overall prevalence of ADHD in adult and adolescent SUD patients. We estimate the prevalence of ADHD among SUD populations at 21%. The estimated prevalence and substantial heterogeneity are consistent with the results of a former meta-analysis from 2012 using similar inclusion and exclusion criteria, but our analysis included more studies and a different meta-analytic approach. Thus, approximately one out of five patients with SUD also suffer from comorbid ADHD in adulthood and adolescents.

By addressing individual SUD populations, we calculated the prevalence of 19% for the cocaine SUD population, 18% for the opioid SUD population, and 25% for the alcohol SUD population. These results suggest that the high prevalence of ADHD in adulthood can be found in SUD populations of all kinds of different substances of use. However, these results should be interpreted with caution since the number of included studies is very low and due to the presence of high heterogeneity in all models.

There are various potential reasons for the substantial heterogeneity in our analysis. One might think about local differences in substance use in ADHD appearance as a reason for this, depending on where the studies were conducted. Other explanations for the heterogeneity might be rater bias, the use of different screening and diagnostic tools, or the determination of different thresholds for the latter. Moreover, diagnosing SUD patients with ADHD is very difficult without intraindividual attention and adjustment to the patients and the in- or outpatient setting.

Moreover, there are many possible screening tools for ADHD among SUD patients that could be considered for daily psychiatric practice. One way to undertake ADHD screening could be the combination of the Wender Utah Rating Scale (WURS-k) for symptoms in childhood and the German self-rating behavior questionnaire (ADHD-SR) for symptoms in adulthood; combined, they have sensitivity of 94% and specificity of 56%. Another method of screening could be the adult ADHD self-report scale v1.1 alone with a sensitivity of 100%, a specificity of 71%, a positive predictive value of 0.52, and a negative predictive value of 1.0. Thus, future studies should investigate which screening tools and which diagnostic procedures are most appropriate and workable for SUD patients in daily practice. Ideally, this should be investigated in a multicentric study design and among different SUD subpopulations, documenting the different substances as specific as possible. Additionally, further scientific efforts should endeavor to determine which therapy concepts are best suited for patients with ADHD and SUD. Established psychological interventions for SUD could be an effective treatment for patients with SUD and ADHD.

Limitations: This meta-analysis suggests that the available data of ADHD in adulthood among SUD populations is very heterogeneous; hence, the current results should be interpreted very cautiously. Furthermore, we were not able to conduct the moderator analysis with the moderator age on the three subpopulations because of the small n among them. For accuracy reasons, we excluded 46 studies only using self-reported questionnaires for confirmation of the diagnosis of ADHD.

5. Conclusions

In today’s psychiatric clinical practice, ADHD in adulthood remains a highly underrated condition, especially when focusing on people suffering from SUD. This meta-analysis shows that every fifth patient suffering from SUD could be diagnosed with a comorbid ADHD if evaluated precisely for research purposes. In order to improve mental health care for this population, new concepts for diagnosis and treatment in daily psychiatric practice in in- and outpatient care must urgently be developed. If diagnosed earlier with ADHD, it is probable that the severity of the course of SUD could be attenuated or even the occurrence itself could be prevented. However, the important question of whether people suffering from ADHD are particularly more susceptible to develop SUD to certain substances unfortunately remains unanswered. Hence, future research efforts should attempt to investigate the prevalence of ADHD among SUD populations for specific substances or substance groups more intensely to address diagnostic and therapeutic means more individually in the future.

Introduction

Substance use disorder (SUD) significantly impacts healthcare systems worldwide. Approximately one in nine hospitalizations in the United States involve patients with SUD, and these numbers have unfortunately increased in recent years. Furthermore, about 28% of all SUD patients die within fifteen years of seeking treatment, with the average age of death being under 50 years. Various substances, such as alcohol, cocaine, and heroin, possess addictive potential.

The progression of SUD is significantly affected by a person's social environment and co-occurring medical or psychiatric conditions. Attention-deficit/hyperactivity disorder (ADHD) is a common comorbidity among SUD patients and is associated with a more severe course of substance use. ADHD is characterized by persistent, age-inappropriate levels of inattention and/or hyperactivity/impulsivity, leading to functional impairment in areas such as work, education, hobbies, family life, social contacts, and self-confidence. While ADHD symptoms typically emerge in childhood, about 40–50% of individuals continue to experience symptoms into adolescence and adulthood, with hyperactivity often diminishing while inattention remains prevalent. Research indicates an ADHD prevalence of 2.5% in adults and 3.4% in childhood, and studies suggest that geographical location and study year do not significantly influence these prevalence estimates.

Patients with ADHD are more prone to developing SUDs at a younger age. A large population-based study demonstrated that ADHD symptoms correlated with a substantially increased risk for alcohol use disorder, illicit drug use, and polysubstance use. Although the precise reason for this heightened association between ADHD and SUD remains unclear, some researchers propose that substance use may represent an attempt to self-medicate ADHD symptoms. Therefore, when treating young adults with co-occurring SUD and ADHD, therapeutic approaches for both disorders should be considered. Medication-only treatment for SUD in ADHD patients with active substance use has not shown high effectiveness. Multimodal therapies, which combine different treatment methods, may be more effective for patients with ADHD and comorbid SUD.

Current data suggest an ADHD prevalence of 21.5% within SUD populations. However, attempts over recent decades to estimate ADHD prevalence among SUD populations have yielded inconsistent data, with estimates varying widely from 5.22% to 62%. Investigations across different SUD populations, involving various substances, indicate an increased prevalence of ADHD in nearly every SUD group. Both stimulant and sedative substances appear to be frequently misused by ADHD patients. Studies involving cocaine users have shown ADHD prevalence rates between 14.5% and 20.5%. Among patients with alcohol addiction, estimated ADHD prevalence ranges from 7.7% to 62%, and among opioid users, an ADHD prevalence of 16.8% has been reported. The most recent meta-analysis available, published in 2012, estimated ADHD prevalence among SUD populations at 23.1%. This analysis also found ADHD prevalence to be 25.3% in adolescents and 21.0% in adults. Despite these findings, routine clinical practice for SUD patients still lacks widespread screening for ADHD. This current meta-analysis was therefore conducted to include more recent studies and more comprehensively highlight the impact of ADHD in SUD.

Objectives This meta-analysis aimed to estimate the prevalence of ADHD among adult SUD patients and within specific SUD subgroups based on different substances. Such an estimate could enhance the understanding of the relationship between these two psychiatric conditions, potentially supporting the need for implementing ADHD screening tools in SUD treatment settings and vice versa.

Materials and Methods

Search Strategies

The structure of this meta-analysis adhered to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) 2020 guideline. Literature searches were conducted in the PUBMED® and Web of Science® databases using the terms [ADHD], [prevalence], and [substance use disorder]. The inclusion period for studies ranged from 1970 to 2022. Reference lists of relevant articles were also examined. The search was performed from 11 May 2022 to 7 July 2022.

Study Selection

The following criteria were used for study inclusion: (1) publication in a peer-reviewed journal, (2) formal diagnosis of SUD according to DSM or ICD criteria, (3) formal diagnosis of ADHD in adults or adolescents according to DSM or ICD criteria (diagnosis based solely on self-report questionnaires was deemed insufficient), and (4) evidence of systematic and sufficient screening for ADHD within SUD populations. Studies were excluded if they (1) only involved secondary data analysis (e.g., systematic reviews), (2) were not available in English or German, or (3) lacked necessary information for the meta-analysis. The risk of bias for included studies was assessed across seven domains, and visualizations of these risks were generated using robvis.

Recorded Variables

Variables extracted from each study included sample size, gender distribution, participants' mean age, ADHD prevalence within the population, and the primary substance of use. For this meta-analysis, only subpopulations of opioid, cocaine, and alcohol users were extracted. Studies where other substances were primary or where primary substance information was missing were categorized as involving various types of substance use. If specific subpopulations were detailed within a study, efforts were made to include them in the analysis. All data extraction and verification were performed by a single researcher.

Meta-Analytic Approach

The meta-analytic procedure was conducted using the R-software library package metafor [version 2.0-0]. A random-effects model, based on logit transformation of individual proportions, was calculated to determine overall prevalence. Inverse variance weighting was applied, and between-study variance was estimated using the Der Simonian Laird method. Heterogeneity was evaluated using Q and I2 statistics. For I2, values of 0.25, 0.50, and 0.75 were interpreted as low, moderate, and high between-trial heterogeneity, respectively. Publication bias was assessed using funnel plots and an Egger intercept test. Additionally, a meta-regression was performed with age as a moderator variable, as age was not a specific inclusion criterion. The same methods were applied to the three SUD subpopulations: cocaine, opioids, and alcohol.

Results

Included Studies and Sample Characteristics

A total of 1691 records were screened, resulting in the inclusion of 31 studies with a combined participant count of 12,524. Specifically, three studies focused on opioid users (n = 2357), seven on cocaine users (n = 2974), and seven on alcohol users (n = 2143) as the primary substance of use. The overall risk of bias across the included studies was estimated as low.

Meta-Analytic Findings

Using a random-effects model, the general prevalence of ADHD among SUD patients was determined to be 21% (95% CI = [0.1741; 0.2548]). Significant heterogeneity was observed (I2 = 95.8%, Q = 721.09; df = 30; p < 0.0001). A moderator analysis for age suggested that age had only a minor influence on heterogeneity (Q (df = 25) = 20.2909, p = 0.7314). Visual inspection of funnel plots and the Egger intercept (z = −1.69, p = 0.30) indicated the absence of publication bias.

While the general prevalence of ADHD among SUD patients was calculated, there were unfortunately very few heterogeneous data points for individual substance subpopulations. Therefore, the following subpopulation data should be interpreted with caution.

For the subpopulation of cocaine users, the calculated ADHD prevalence was 19% (95% CI = [0.1058; 0.3102]), also exhibiting significant heterogeneity (I2 = 96.7%, Q = 238.89; df = 8; p < 0.0001). Among opioid users, the calculated ADHD prevalence was 18% (95% CI = [0.0784; 0.3505]), with significant heterogeneity present (I2 = 97.4%, Q = 153.26; df = 4; p < 0.0001).

For the subpopulation of individuals with alcohol addiction, the calculated ADHD prevalence was 25% (95% CI = [0.1845; 0.3360]), accompanied by significant heterogeneity (I2 = 92.5%, Q = 106.55; df = 8; p < 0.0001). Due to the small sample sizes within these subpopulations, a moderator analysis for age could not be conducted.

Discussion

Our primary objective was to estimate the overall prevalence of ADHD in adult and adolescent SUD patients. This analysis estimates the prevalence of ADHD among SUD populations at 21%. This estimated prevalence and the substantial heterogeneity observed are consistent with findings from a prior meta-analysis published in 2012, even with the inclusion of more recent studies and a different analytical approach. Thus, approximately one in five patients with SUD also experience comorbid ADHD in adulthood and adolescence.

When examining individual SUD populations, the prevalence of ADHD was calculated at 19% for cocaine SUD, 18% for opioid SUD, and 25% for alcohol SUD. These results suggest that the high prevalence of ADHD in adulthood extends across SUD populations involving various types of substances. However, these findings should be interpreted with caution due to the limited number of included studies for each subpopulation and the presence of high heterogeneity across all models.

The substantial heterogeneity observed in this analysis could stem from various factors. Potential reasons include localized differences in substance use patterns or ADHD presentation depending on the study's geographical location. Other explanations for heterogeneity might involve differences in rater interpretation, the use of various screening and diagnostic tools, or differing diagnostic thresholds. Moreover, diagnosing ADHD in SUD patients presents a significant challenge, often requiring individualized attention and adaptation to the patient's specific inpatient or outpatient setting.

Numerous potential screening tools for ADHD among SUD patients could be considered for routine psychiatric practice. One approach for ADHD screening could involve combining the Wender Utah Rating Scale (WURS-k) for childhood symptoms with the German self-rating behavior questionnaire (ADHD-SR) for adult symptoms; together, these instruments demonstrate high sensitivity and moderate specificity. Another screening method is the adult ADHD self-report scale v1.1 alone, which shows high sensitivity, moderate specificity, and strong negative predictive value. Future studies should therefore investigate which screening tools and diagnostic procedures are most appropriate and practical for SUD patients in daily clinical settings. Ideally, this research should utilize a multicenter study design across different SUD subpopulations, meticulously documenting specific substances involved. Additionally, further scientific efforts are needed to determine the most effective therapy concepts for patients with co-occurring ADHD and SUD. Established psychological interventions for SUD may prove effective for patients with both SUD and ADHD.

Limitations This meta-analysis indicates that the available data on adult ADHD within SUD populations is highly heterogeneous, requiring cautious interpretation of the current results. Furthermore, it was not possible to conduct a moderator analysis with age for the three subpopulations due to their small sample sizes. For reasons of accuracy and reliability, 46 studies that relied solely on self-reported questionnaires for ADHD diagnosis were excluded.

Conclusions

In contemporary psychiatric clinical practice, adult ADHD often remains an underestimated condition, particularly in individuals suffering from SUD. This meta-analysis demonstrates that approximately one in five patients with SUD could be diagnosed with comorbid ADHD if precisely evaluated for research purposes. To improve mental health care for this population, new diagnostic and treatment strategies for routine inpatient and outpatient psychiatric practice must be urgently developed. If ADHD is diagnosed earlier, it is probable that the severity of SUD progression could be lessened, or its onset potentially prevented. However, the crucial question of whether individuals with ADHD are particularly susceptible to developing SUD for certain substances remains unanswered. Therefore, future research efforts should aim to more intensely investigate the prevalence of ADHD among SUD populations for specific substances or substance groups, allowing for more individualized diagnostic and therapeutic approaches in the future.

Introduction

The global healthcare system is significantly affected by addiction. In the United States, about one in nine hospitalizations involve patients diagnosed with substance use disorder (SUD). These numbers have unfortunately risen in recent years. Tragically, around 28% of individuals with SUD pass away within fifteen years of beginning treatment, often before the age of 50. Various substances, such as alcohol, cocaine, and heroin, possess addictive properties.

The progression of SUD is significantly shaped by a person's social environment and co-occurring medical or psychiatric conditions. Attention-Deficit/Hyperactivity Disorder (ADHD) is frequently observed alongside SUD, often leading to a more severe progression of substance use. ADHD involves ongoing patterns of inattention, hyperactivity, or impulsivity that are not typical for a person's age. These patterns can interfere with work, education, hobbies, family life, social interactions, and self-confidence. While ADHD symptoms usually appear during childhood, about 40–50% of individuals continue to experience symptoms into adolescence and adulthood, with inattention often persisting more than hyperactivity. Studies indicate that ADHD affects about 2.5% of adults and 3.4% of children. A broad analysis also found that ADHD prevalence estimates did not vary based on geographic location or the year a study was conducted.

Individuals with ADHD tend to develop SUDs at an earlier age. A substantial population study revealed that ADHD symptoms were linked to a significantly higher risk for alcohol use disorder, illicit drug use, and the use of multiple substances. The exact reason for this strong connection between ADHD and SUD is not fully understood, though some researchers propose that substance use might be an attempt to self-medicate ADHD symptoms. Therefore, treatment plans for young adults with co-occurring SUD and ADHD should consider strategies for both conditions. Medications alone do not seem to be highly effective for treating SUD in ADHD patients who are actively using substances. Instead, multimodal therapies, which combine different treatment approaches, may offer more effective results for patients with both ADHD and SUD.

Current information suggests that 21.5% of individuals with SUD also have ADHD. Over recent decades, numerous efforts to estimate ADHD prevalence among SUD populations have yielded inconsistent data, with figures varying widely from 5.22% to 62%. Research across different types of SUDs, involving various substances, indicates an elevated ADHD prevalence in nearly all SUD groups. Individuals with ADHD appear to frequently misuse both stimulant and sedative substances. For example, studies of cocaine users show ADHD prevalence between 14.5% and 20.5%. Among those with alcohol addiction, estimated ADHD prevalence ranges from 7.7% to 62%, and among opioid users, it was found to be 16.8%. The most recent comprehensive analysis prior to this study, published in 2012, estimated ADHD prevalence among SUD populations at 23.1%. That analysis also reported ADHD prevalence of 25.3% in adolescents and 21.0% in adults. Despite these findings, routine clinical practice for SUD patients does not typically include ADHD screening. This new meta-analysis was undertaken to incorporate recent studies and more thoroughly emphasize the impact of ADHD in SUD.

The primary goal of this meta-analysis was to estimate the prevalence of ADHD among adult SUD patients and within specific SUD groups linked to different substances. This research aimed to enhance understanding of the relationship between these two distinct psychiatric conditions, thereby informing discussions about the potential need for routine ADHD screening in SUD treatment settings, and vice versa.

Materials and Methods

2.1. Search Strategies

The design of this meta-analysis followed the PRISMA 2020 guideline for systematic reviews. A literature search was conducted in the PUBMED® and Web of Science® databases. The search terms used were "ADHD," "prevalence," and "substance use disorder." Studies published between 1970 and 2022 were considered for inclusion. Reference lists from identified articles were also reviewed. The search process occurred from May 11, 2022, to July 7, 2022.

2.2. Study Selection

Studies were included if they met the following criteria: published in a peer-reviewed journal; involved a formal diagnosis of SUD based on DSM or ICD criteria; included a formal diagnosis of ADHD in adults or adolescents using DSM or ICD criteria (self-report questionnaires alone were not sufficient for diagnosis); and performed systematic and adequate screening among SUD populations. Studies were excluded if they only involved secondary analysis of data (such as systematic reviews), were not available in English or German, or lacked essential information for the meta-analysis. A visual diagram provides an overview of the study selection process. The risk of bias for each included study was evaluated across seven areas, and a specialized tool called robvis was used to generate visual summaries of these assessments.

2.3. Recorded Variables

The data collected from each study included the number of participants, the distribution of genders, the average age of participants, the reported prevalence of ADHD within the study population, and the primary substance of use. For this meta-analysis, information was specifically extracted for groups of opioid, cocaine, and alcohol users. Studies where other substances were the primary focus or where the main substance was not specified were categorized as involving various types of substance use. If a study detailed specific subgroups, efforts were made to include this information in the analysis. One researcher was responsible for extracting and verifying all data from each study.

2.4. Meta-Analytic Approach

The meta-analysis was performed using the metafor package [version 2.0-0] in R-software. A random-effects model was employed to calculate the overall proportion, based on a logit transformation of individual study proportions. Inverse variance weighting was applied, and the Der Simonian Laird estimator was used to determine the variance between studies. Differences between study results (heterogeneity) were evaluated using Q and I2 statistics. For I2, values of 0.25, 0.50, and 0.75 indicated low, moderate, and high variability between studies, respectively. Potential publication bias was examined using funnel plots and an Egger intercept. Additionally, because age was not a specific inclusion criterion, a meta-regression was conducted using age as a moderating variable. The same analytical methods were applied to the three specific SUD subgroups: cocaine users, opioid users, and alcohol users.

Results

3.1. Included Studies and Sample Characteristics

A total of 1691 records were initially screened, leading to the inclusion of 31 studies comprising 12,524 participants. Among these, three studies focused on opioid users (2,357 participants), seven on cocaine users (2,974 participants), and seven on alcohol users (2,143 participants) as their primary substance of use. A list of all included studies is provided in Table 1. The overall risk of bias across the included studies was assessed as low, as illustrated in Figures 2 and 3.

3.2. Meta-Analytic Findings

Using a random-effects model, the overall prevalence of ADHD among SUD patients was determined to be 21% (with a 95% confidence interval ranging from 17.41% to 25.48%). Substantial variation was observed across studies (I2 = 95.8%, p < 0.0001). An analysis exploring age as a potential factor influencing this variation indicated that age had only a minor impact. Visual inspection of statistical plots suggested that publication bias was not a significant concern (Figure 4 and Figure 5 illustrate these findings).

While a general prevalence for ADHD among SUD patients was calculated, the data for specific substance subgroups were limited and highly varied. Therefore, the findings for these subgroups should be interpreted with caution.

For cocaine users, the calculated ADHD prevalence was 19% (95% CI = [10.58%; 31.02%]), also showing significant variation between studies (I2 = 96.7%, p < 0.0001). Among opioid users, the estimated ADHD prevalence was 18% (95% CI = [7.84%; 35.05%]), with considerable heterogeneity (I2 = 97.4%, p < 0.0001). For individuals with alcohol use disorder, ADHD prevalence was calculated at 25% (95% CI = [18.45%; 33.60%]), again with significant variability (I2 = 92.5%, p < 0.0001). Figures 6, 7, and 8 provide detailed plots for these subpopulations. A moderator analysis using age could not be performed for these subgroups due to the small number of studies within each.

Discussion

The primary objective of this study was to estimate the overall prevalence of ADHD in adult and adolescent patients with SUD. The analysis estimates that 21% of individuals in SUD populations have co-occurring ADHD. This estimated prevalence and the significant variability observed across studies align with findings from a previous meta-analysis published in 2012. However, the current analysis incorporates a larger number of studies and a distinct meta-analytic methodology. These results indicate that roughly one in five adult and adolescent patients with SUD also experience ADHD.

When examining specific SUD populations, the prevalence of ADHD was calculated at 19% for cocaine users, 18% for opioid users, and 25% for alcohol users. These findings suggest that a high prevalence of adult ADHD is present across various types of substance use. Nevertheless, these specific results should be interpreted carefully due to the limited number of studies included for each substance subgroup and the substantial variability observed within all models.

Several potential factors may contribute to the considerable variability observed in this analysis. Differences in regional substance use patterns or ADHD presentation based on study location could be one reason. Other explanations for this variability include potential biases from evaluators, the use of different screening and diagnostic instruments, or variations in the diagnostic thresholds applied. Furthermore, accurately diagnosing ADHD in patients with SUD presents a challenge, often requiring individualized attention and adaptation to whether the patient is in an inpatient or outpatient setting.

Numerous screening tools for ADHD exist that could be considered for routine psychiatric practice with SUD patients. One potential approach involves combining the Wender Utah Rating Scale (WURS-k) to assess childhood symptoms and the German self-rating behavior questionnaire (ADHD-SR) for adult symptoms; together, these tools offer 94% sensitivity and 56% specificity. Another screening option is the adult ADHD self-report scale v1.1 used independently, which provides 100% sensitivity, 71% specificity, a positive predictive value of 0.52, and a negative predictive value of 1.0. Future research should explore which screening tools and diagnostic procedures are most suitable and practical for SUD patients in daily clinical settings. Ideally, such investigations would involve multi-center studies across various SUD subgroups, meticulously documenting specific substances involved. Further scientific efforts are also needed to identify the most effective therapeutic approaches for patients with both ADHD and SUD. Existing psychological interventions for SUD may prove beneficial for this patient population.

This meta-analysis has several limitations. The existing data on adult ADHD within SUD populations are highly varied, meaning the current findings should be interpreted with significant caution. Additionally, it was not possible to perform a moderator analysis using age for the three specific substance subgroups due to the limited number of studies in each. To ensure diagnostic accuracy, 46 studies that relied solely on self-reported questionnaires for ADHD diagnosis were excluded from this analysis.

Conclusions

In current psychiatric clinical practice, adult ADHD remains a frequently overlooked condition, particularly among individuals with SUD. This meta-analysis indicates that, with careful evaluation for research purposes, approximately one in five SUD patients could also be diagnosed with co-occurring ADHD. To enhance mental healthcare for this population, it is crucial to urgently develop new diagnostic and treatment strategies for routine psychiatric practice, in both inpatient and outpatient settings. Earlier diagnosis of ADHD might potentially lessen the severity of SUD progression or even prevent its onset.

However, the critical question of whether individuals with ADHD are particularly more prone to developing SUDs involving specific substances remains unanswered. Therefore, future research should more intensely investigate the prevalence of ADHD within SUD populations for specific substances or substance groups to allow for more individualized diagnostic and therapeutic approaches moving forward.

Introduction

Substance use disorder (SUD), or addiction, significantly affects healthcare systems globally. In the United States, about one in nine hospital stays involves patients with SUD, and these numbers have been rising. Sadly, around 28% of individuals with SUD die within 15 years of starting treatment, often before age 50. Many substances, such as alcohol, cocaine, and heroin, can lead to addiction.

How SUD progresses is greatly shaped by a person's social setting and other health conditions, both physical and mental. Attention-Deficit/Hyperactivity Disorder (ADHD) is a common condition found with SUD, often leading to more severe substance use. ADHD involves ongoing difficulty with focus, or being overly active and impulsive, which affects work, school, hobbies, family, and self-confidence. While ADHD often starts in childhood, about 40–50% of people continue to have symptoms into their teenage and adult years, though hyperactivity may lessen while inattention remains. Studies indicate ADHD affects about 2.5% of adults and 3.4% of children. Research also suggests that the location or year a study was done does not change how often ADHD is reported.

Individuals with ADHD tend to develop SUDs earlier in life. A large study also found that ADHD symptoms were linked to a higher risk of alcohol use disorder, illegal drug use, and using multiple substances. The exact reason for this connection is not known, though some experts believe people may use substances to try and manage their ADHD symptoms. Therefore, when treating young adults who have both SUD and ADHD, treatment plans for both conditions should be considered. Medication by itself does not seem very effective for treating SUD in ADHD patients who are actively using substances. A combination of different therapies, called multimodal therapies, might be more effective for patients with ADHD and SUD.

Current information suggests that about 21.5% of people with SUD also have ADHD. Over recent decades, many efforts have been made to estimate ADHD rates among those with SUD, but the results have varied widely, from 5.22% to 62%. Studies focusing on different types of substance addictions show that higher rates of ADHD are present in almost all SUD groups. Individuals with ADHD often misuse both stimulant and sedative substances. For example, studies of cocaine users have found ADHD rates between 14.5% and 20.5%. Among those with alcohol addiction, ADHD rates have ranged from 7.7% to 62%, and for opioid users, the rate was shown to be 16.8%. A meta-analysis from 2012 estimated the overall ADHD rate among SUD populations at 23.1%, with 25.3% in adolescents and 21.0% in adults. Despite these findings, there is still no routine screening for ADHD in the daily treatment of SUD patients. This new meta-analysis was therefore conducted to include recent studies and better understand the effect of ADHD on SUD.

The primary goal of this meta-analysis was to estimate how often ADHD occurs in adult SUD patients and in different groups of SUD patients based on the substance used. This research aims to improve understanding of the link between these two mental health conditions. Such understanding could highlight the need for screening tools to identify ADHD in those with SUD, and vice versa.

Materials and Methods

This meta-analysis followed the PRISMA 2020 guideline, a standard for reporting systematic reviews. Researchers searched the PUBMED® and Web of Science® databases between May 11 and July 7, 2022, for studies published from 1970 to 2022. They used search terms like [ADHD], [prevalence], and [substance use disorder]. Reference lists from relevant articles were also checked.

Studies were included if they were published in peer-reviewed journals, formally diagnosed SUD and ADHD in adults or adolescents using recognized criteria (like DSM or ICD), and had conducted systematic screening among SUD populations. Studies were excluded if they were secondary analyses (like other reviews), not in English or German, or lacked necessary information. The risk of bias in the included studies was assessed using seven factors.

Information gathered from each study included the number of participants, gender breakdown, average age, how often ADHD was found, and the main substance used. For this analysis, specific attention was paid to groups using opioids, cocaine, and alcohol. If a study involved other substances or did not specify the main substance, it was categorized as 'various types of substance use.' One researcher extracted and verified all data.

The statistical analysis was performed using R-software. A random-effects model was used to calculate overall rates, considering differences between studies. Methods were also applied to the three specific SUD groups: cocaine, opioids, and alcohol.

Results

From an initial 1691 records, 31 studies were included in this analysis, involving a total of 12,524 participants. Among these, three studies focused on opioid users (2,357 participants), seven on cocaine users (2,974 participants), and seven on alcohol users (2,143 participants). The overall risk of bias in these studies was considered low.

Based on the meta-analysis, the general rate of ADHD among SUD patients was found to be 21% (with a 95% confidence interval of 17.41% to 25.48%). There was significant variation across the studies, meaning the results were not very consistent. A further analysis suggested that participant age had only a minor impact on these differences. No evidence of publication bias was found, suggesting that studies with certain results were not more likely to be published than others.

While an overall prevalence of ADHD in SUD patients was calculated, data for specific substance groups were limited and varied widely. Therefore, these specific results should be viewed with caution. For the group of cocaine users, the estimated ADHD prevalence was 19% (ranging from 10.58% to 31.02%). For opioid users, it was 18% (ranging from 7.84% to 35.05%). For alcohol users, the estimated ADHD prevalence was 25% (ranging from 18.45% to 33.60%). Significant differences between studies were also present within each of these substance-specific groups. Due to the small number of studies in these specific subgroups, a detailed analysis considering age as a factor could not be performed.

Discussion

The main goal of this study was to estimate the overall rate of ADHD in adult and adolescent SUD patients. The analysis estimated that ADHD affects about 21% of individuals in SUD populations. This finding and the notable differences among studies are similar to a previous meta-analysis from 2012. However, this current study included more recent research and used a different statistical approach. This means that roughly one out of every five patients with SUD, whether adults or adolescents, also has ADHD.

By looking at specific SUD groups, the estimated ADHD rates were 19% for cocaine users, 18% for opioid users, and 25% for alcohol users. These results suggest that ADHD is common across many different types of substance use. However, these specific figures should be interpreted carefully because only a small number of studies were included for each substance, and there were large differences between those studies.

The significant variation among the studies in this analysis could be due to several factors. Differences in substance use patterns in different locations where studies were conducted might play a role. Other explanations include potential biases from the researchers, the use of various screening and diagnostic tools, or different criteria for diagnosing ADHD. Diagnosing ADHD in patients with SUD can also be difficult without careful, individualized assessment, considering whether the patient is receiving inpatient or outpatient care.

Several screening tools exist that could be useful for identifying ADHD in SUD patients in everyday clinical practice. For instance, combining the Wender Utah Rating Scale (WURS-k) for childhood symptoms and the German self-rating behavior questionnaire (ADHD-SR) for adult symptoms has shown good accuracy. Another option is the adult ADHD self-report scale v1.1 alone, which also performs well. Future research should explore which screening tools and diagnostic methods are most suitable and practical for SUD patients in real-world settings. Ideally, such studies would involve multiple centers and look at different types of SUD, noting the specific substances used. Additionally, more scientific effort is needed to determine the best treatment approaches for patients with both ADHD and SUD. Standard psychological treatments for SUD might also be effective for those with co-occurring ADHD.

This meta-analysis highlights that the available information on adult ADHD among SUD populations varies greatly, so the results should be considered with caution. Another limitation was that a detailed analysis, looking at age as a factor, could not be performed for the specific substance groups due to the small number of studies in those categories. Furthermore, 46 studies that relied only on self-reported questionnaires for ADHD diagnosis were excluded to ensure accuracy.

Conclusions

In current mental health practice, adult ADHD is often overlooked, especially in people who have substance use disorder. This meta-analysis indicates that one in five patients with SUD might also be diagnosed with ADHD if they were thoroughly assessed for research purposes. To improve care for this group, new methods for diagnosis and treatment in daily clinical practice, both in hospitals and outpatient clinics, are urgently needed.

If ADHD were diagnosed earlier, it is likely that the severity of a person's SUD could be reduced, or perhaps the SUD itself could even be prevented. However, an important question remains unanswered: whether people with ADHD are more likely to develop SUDs involving certain substances. Future research should focus more intensely on how often ADHD occurs among specific substance users or groups of substances. This deeper understanding could help tailor diagnostic approaches and treatments more effectively in the future.

1. Introduction

Addiction causes many problems in healthcare around the world. In the United States, about one in nine hospital visits are for people with a substance use problem. Sadly, these numbers have been growing. Also, about 28 out of every 100 people with a substance use problem die within 15 years of getting help, often before they turn 50. Many different substances can be addictive, such as alcohol, cocaine, or heroin.

A person's social life and other health problems, both physical and mental, greatly affect their substance use. Attention Deficit Hyperactivity Disorder (ADHD) is a common mental health problem seen in people with substance use issues. When a person has both, their substance use is often more serious. ADHD means a person has ongoing trouble paying attention, and/or they are very active or act without thinking, more than is normal for their age. These problems can make it hard to do well at work, in school, or with hobbies. They can also affect family life, friendships, and how a person feels about themselves. Usually, ADHD signs show up when a person is a child. However, about 40 to 50 out of every 100 children with ADHD still have signs in their teen years and as adults. Often, being overly active lessens, but trouble paying attention stays common. Studies show that about 2.5 out of 100 adults and 3.4 out of 100 children have ADHD. Research also shows that where a study was done or the year it was done did not change how many people were found to have ADHD.

People with ADHD are more likely to develop substance use problems at a younger age. A large study of many people showed that having ADHD signs was linked to a much higher chance of having problems with alcohol, using illegal drugs, and using many different substances. The exact reason why ADHD and substance use problems are so connected is not fully known. Some experts think people might use substances to try to help their ADHD signs. Because of this, when treating young adults with substance use problems and ADHD, doctors should think about ways to treat both issues. Using only medicine may not work well to treat substance use problems in people with active substance use who also have ADHD. Using many different types of treatment together may work better for people with both ADHD and substance use problems.

Current information shows that about 21.5 out of 100 people with substance use problems also have ADHD. Over the past decades, many efforts were made to guess how many people with substance use problems also have ADHD. The numbers found in studies were very different, ranging from about 5 out of 100 to 62 out of 100. Studies of different groups of people addicted to different substances show that more people have ADHD in almost every group with substance use problems. Both drugs that speed up the body and drugs that slow it down seem to be used often by people with ADHD. Studies on people who use cocaine show that between 14.5 and 20.5 out of 100 have ADHD. In groups of people with alcohol addiction, studies found that between 7.7 and 62 out of 100 had ADHD, and among people who use opioids, 16.8 out of 100 had ADHD. The newest large review of many studies that is known was published in 2012. It estimated that 23.1 out of 100 people with substance use problems also had ADHD. The review also showed that 25.3 out of 100 teens and 21 out of 100 adults with substance use problems had ADHD. But even now, doctors usually do not check for ADHD in people with substance use problems. Because of this, researchers decided to do a new large review of studies, including the most recent ones, to better show how much ADHD affects substance use problems.

Objectives

This large review of studies wanted to find out how many adults with substance use problems also have ADHD, including those who use different substances. This could help people better understand the link between these two mental health conditions. It could also show if it is important to start checking for ADHD in people with substance use problems, and for substance use problems in people with ADHD.

2. Materials and Methods

Search Strategies

This large review of studies followed a set of guidelines for careful research. Researchers looked through health databases like PUBMED® and Web of Science®. They searched for terms like "ADHD," "prevalence," and "substance use disorder." They looked at studies published between 1970 and 2022. They also looked at the lists of references in the studies they found. The search was done from May 11, 2022, to July 7, 2022.

Study Selection

The following rules were used to pick studies: (1) the study had to be published in a trusted medical journal, (2) substance use problems had to be officially diagnosed using standard medical guidelines, (3) ADHD in adults or teens had to be officially diagnosed using standard medical guidelines (diagnosis based only on a person saying they have it was not enough), and (4) the study had to show that proper checks for ADHD were done among people with substance use problems. The following studies were not included: (1) studies that only used old information (like other large reviews of studies), (2) studies not written in English or German, and (3) studies that did not have enough information for this large review. Researchers checked for possible problems or biases in the studies chosen.

Recorded Variables

From each study, researchers wrote down information like the number of people in the study, how many were male or female, the average age of the people, how many people had ADHD, and the main substance they used. For this study, only groups of people who mainly used opioids, cocaine, or alcohol were looked at. Studies where people used other main substances, or where the main substance was not clear, were put into a group called "various types of substance use." If a study had smaller groups of people who used specific substances, researchers tried to use that information. One researcher collected and checked all the information from each study.

Meta-Analytic Approach

The process of combining all the study results was done using a special computer program. A model was used that allowed for differences between studies to be considered. This helped to find the overall percentage of people with ADHD. Different ways were used to see how much the studies differed from each other. Researchers also checked for any unfairness in what was published, like if studies with certain results were more likely to be published. They also looked at how age might affect the results, since there was no specific age limit for who could be in the studies. The same methods were used for the three groups of people who used specific substances: cocaine, opioids, and alcohol.

3. Results

Included Studies and Sample Characteristics

Researchers looked at 1,691 records and included 31 studies with a total of 12,524 participants. This included three studies on opioid users (2,357 people), seven studies on cocaine users (2,974 people), and seven studies on alcohol users (2,143 people). Overall, the studies included had a low risk of being unfair or biased.

Meta-Analytic Findings

Using a special model, researchers found that about 21 out of 100 people with substance use problems also have ADHD. There were big differences between the studies. An analysis looking at age showed that age had only a small effect on these differences. Looking at the results, there was no sign that studies with certain outcomes were more likely to be published.

While the general rate of ADHD among people with substance use problems could be calculated, there was not much information for groups of people who used specific substances. Because of this, the following numbers should be viewed with care.

For people who used cocaine, about 19 out of 100 had ADHD. There were big differences between the studies. For people who used opioids, about 18 out of 100 had ADHD. Again, there were big differences between the studies. For people with alcohol problems, about 25 out of 100 had ADHD. There were also big differences among these studies. Because there were so few studies in these specific groups, researchers could not do more detailed analyses about age for these groups.

4. Discussion

The main goal was to find out how many adults and teens with substance use problems also have ADHD. This study estimates that about 21 out of 100 people with substance use problems also have ADHD. This number, and the big differences found between studies, is similar to what a previous large review from 2012 found. That means about one in five people with substance use problems in adulthood and their teen years also suffer from ADHD.

When looking at people who used specific substances, the study found that about 19 out of 100 cocaine users, 18 out of 100 opioid users, and 25 out of 100 alcohol users had ADHD. These results suggest that a high number of adults with ADHD can be found in groups of people who use all different kinds of substances. However, these results should be looked at carefully because there were not many studies included for each substance, and there were large differences between the studies.

There could be many reasons for the differences found in this study. For example, there might be local differences in substance use or how ADHD appears, depending on where the studies were done. Other reasons for the differences could be how the people doing the study rated things, or that different tools and rules were used to check for and diagnose ADHD. Also, it can be very hard to diagnose ADHD in people with substance use problems without carefully paying attention to each person and adapting to whether they are getting care in a hospital or as an outpatient.

There are many ways to check for ADHD in people with substance use problems that could be used in daily medical practice. One way could be to use two surveys together: one about childhood ADHD signs and one about adult ADHD signs. Another way could be to use just one survey for adults. Future studies should look into which checking tools and ways of diagnosing ADHD work best for people with substance use problems in daily practice. Ideally, this should be studied in many different places and among different groups of people who use various substances, making sure to record the substances as specifically as possible. Also, more scientific work should try to find out which treatment plans work best for people with both ADHD and substance use problems. Current types of talk therapy for substance use problems could be helpful for people with both conditions.

Limitations

This large review of studies suggests that the information available about ADHD in adults with substance use problems is very different from study to study. Because of this, the current results should be looked at very carefully. Also, researchers could not do more detailed analyses about age in the three groups of specific substance users because there were too few studies in those groups. For more accurate results, 46 studies that only used self-reported surveys to confirm an ADHD diagnosis were not included.

5. Conclusions

In today's mental health care, ADHD in adults often goes unnoticed, especially in people who have substance use problems. This large review of studies shows that if checked carefully for research, about one in five people with substance use problems could also be diagnosed with ADHD. To improve mental health care for these people, new ways to diagnose and treat them in daily practice, both in hospitals and as outpatients, are urgently needed. If ADHD is diagnosed earlier, it is likely that substance use problems might not be as severe, or perhaps even prevented. However, the important question of whether people with ADHD are more likely to develop substance use problems with certain substances sadly remains unanswered. So, future research should try to study how many people with ADHD also have substance use problems related to specific substances or groups of substances more closely. This would help in making diagnoses and treatments more suited to each person in the future.