A small retrospective study of 67 adults with ADHD found that those who also had alcohol or cannabis use disorders were far less likely to respond to standard ADHD medications. While these findings are preliminary and cannot prove causation, they highlight a gap in care for patients whose substance use may complicate ADHD treatment outcomes in everyday clinical settings.

Most ADHD pharmacotherapy trials systematically exclude patients with active substance use disorders, creating a significant blind spot for clinicians who routinely treat exactly these individuals. In real-world practice, ADHD frequently co-occurs with alcohol and cannabis use disorders, and clinicians lack robust evidence about how these comorbidities affect treatment response. This study directly engages that gap, offering early observational signal about which patients may need closer monitoring, modified treatment strategies, or integrated care approaches when standard ADHD medications are prescribed.

ADHD in adults is frequently accompanied by psychiatric and substance use comorbidities that complicate treatment. While stimulant and non-stimulant pharmacotherapy has a well-established evidence base in “clean” clinical trial populations, the degree to which real-world comorbidities modify treatment response remains poorly characterized. This Italian retrospective cohort study sought to identify clinical predictors of non-response among adults with DSM-5-TR-confirmed ADHD receiving routine pharmacological care at a specialized psychiatric outpatient clinic. The researchers specifically examined whether comorbid alcohol use disorder, cannabis use disorder, and autism spectrum disorder were associated with reduced odds of achieving a meaningful clinical response, defined by a Clinical Global Impression-Improvement (CGI-I) score of 1 to 3.

Among 67 enrolled adults, 71.6% achieved clinical response. Using exploratory binary logistic regression with parsimonious multivariable models, alcohol use disorder was associated with approximately 90 to 92% lower odds of response (OR approximately 0.08 to 0.10, p = 0.010 to 0.026), and cannabis use disorder was associated with approximately 76 to 80% lower odds (OR approximately 0.20 to 0.24, p = 0.014 to 0.028). These associations were consistent across the models tested. Autism spectrum disorder showed a descriptive trend toward lower response rates but did not reach stable statistical significance after adjustment. The authors appropriately acknowledge that the single-center retrospective design, small sample, and absence of a control group preclude causal inference. They call for larger, prospective studies to validate these findings and inform integrated treatment approaches.

This study asks a question that most of us in clinical practice have already noticed anecdotally: patients with ADHD who also carry substance use diagnoses tend to have a harder time getting better on standard medications. The strength here is that the researchers studied exactly the kind of patient population that randomized trials typically exclude. The limitation is also apparent: with only 67 patients, a single site, and no control group, the odds ratios are alarmingly wide, and we cannot confidently distinguish whether the substance use disorders themselves are blunting medication effect, whether these patients have more severe or treatment-resistant ADHD, or whether unmeasured behavioral and adherence factors are driving the signal.

In my own practice, I treat ADHD and substance use as intertwined conditions that demand simultaneous attention rather than sequential management. I pay close attention to cannabis use patterns in particular, because patients sometimes self-medicate ADHD symptoms with cannabis and may resist changing that pattern when we introduce pharmacotherapy. I use this kind of evidence not as a prescriptive protocol but as a clinical flag to monitor more closely, reassess treatment goals earlier, and have honest conversations about how substance use may be interacting with the medications we prescribe.

This study sits early in the research arc for understanding how substance use comorbidities modify ADHD pharmacotherapy outcomes in adults. While the broader literature has long recognized the high overlap between ADHD and substance use disorders, most treatment evidence comes from trials that exclude these patients. The current findings therefore represent a hypothesis-generating contribution rather than practice-changing evidence. Clinicians should interpret the dramatic odds ratios with caution, as these reflect the instability inherent in small-sample logistic regression rather than precise effect quantification.

From a pharmacological standpoint, both alcohol and cannabis have known effects on dopaminergic and noradrenergic neurotransmission, the same pathways targeted by stimulant and non-stimulant ADHD medications. Chronic alcohol use may alter receptor sensitivity, while cannabis use may affect executive function through overlapping but distinct mechanisms. There are also practical considerations around medication adherence, substance-related cognitive impairment, and the potential for stimulant diversion in populations with active substance use disorders. The most actionable recommendation from this evidence is to screen all adult ADHD patients for active alcohol and cannabis use disorders at baseline and to establish shorter follow-up intervals and more structured response assessments for those with confirmed comorbid substance use.

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