Heavy cannabis use associated with worse cognitive outcomes in ADHD patients | Research

The takeaway

Among 50 ADHD patients, those with heavy cannabis use scored significantly lower on objective cognitive testing and showed more severe hyperactivity compared to ADHD patients without substance use disorders.

Psychiatrists, ADHD patients, and anyone interested in how cannabis use interacts with attention and cognitive disorders.

Heavy cannabis use + ADHD linked to significantly lower cognitive scores (P = 0.0011)

What the researchers found

ADHD patients with comorbid substance use disorders scored significantly lower on objective cognitive testing (IVA/CPT, P < 0.0001). When groups were split by heavy cannabis use specifically, the association with poorer outcomes was even more pronounced, including lower cognitive scores (P = 0.0011), more severe fine motor hyperactivity, and higher self-reported hyperactivity/impulsivity (P = 0.0088 and 0.0172).

Why it matters

ADHD and substance use disorders frequently co-occur, but how they interact is poorly understood. This study suggests heavy cannabis use may compound the cognitive difficulties already present in ADHD.

The numbers in context

50 ADHD patients; SUD group IVA/CPT scores P < 0.0001 lower; heavy cannabis subgroup: cognitive P = 0.0011, fine motor hyperactivity significant, self-reported hyperactivity P = 0.0088

How the study worked

Researchers retrospectively analyzed 50 ADHD patient charts, allocated by substance use disorder status, then performed subgroup analysis by heavy cannabis use. Mann-Whitney and chi-square tests compared cognitive testing scores and functional outcomes.

What this study cannot tell us

Very small sample of 50 patients. Retrospective chart review. Single institution. Cannot determine causation. No control for ADHD medication status or other confounders.

How to read the evidence

Very small retrospective chart review with no ability to determine causation, though the specific focus on ADHD-cannabis interaction fills a gap.

When this study was published

Published in 2021.

The bigger picture

Whether cannabis worsens ADHD symptoms or people with more severe ADHD are more likely to use cannabis heavily remains an open question. This study cannot determine direction of causation but highlights the clinical importance of assessing cannabis use in ADHD patients.

Questions still open

Does cannabis directly impair cognition in ADHD, or do patients with worse ADHD self-medicate more heavily? Would reducing cannabis use improve cognitive test scores? How should clinicians approach cannabis use in ADHD patients who report symptom relief?

Common questions

Did cannabis make ADHD worse?

The study found an association between heavy cannabis use and worse ADHD cognitive outcomes, but cannot determine whether cannabis caused the worse outcomes or whether people with more severe ADHD were more likely to use cannabis.

Was heavy cannabis use worse than other substance use?

Yes. When patients were grouped by heavy cannabis use specifically rather than general substance use disorder status, the associations with poorer cognitive and hyperactivity outcomes were more pronounced.

Read the original research

Naturalistic exploratory study of the associations of substance use on ADHD outcomes and function.

BMC psychiatry, 21(1), 251

View on PubMed ↗Publisher’s paper ↗

Citation

MacDonald, Benjamin; Sadek, Joseph. (2021). Naturalistic exploratory study of the associations of substance use on ADHD outcomes and function.. BMC psychiatry, 21(1), 251. https://doi.org/10.1186/s12888-021-03263-6