A childhood ADHD diagnosis was associated with executive function deficits in young adults, but current regular cannabis use was not, though early cannabis initiation before age 16 may matter.
Read this if you have ADHD and use cannabis and want to know whether it compounds your cognitive challenges.
ADHD drove cognitive deficits; adult cannabis use added no measurable impairment
What the researchers found
Researchers compared cognitive performance in young adults (average age 24) across four groups: those with childhood ADHD who used cannabis, those with ADHD who did not, non-ADHD cannabis users, and non-ADHD non-users. After controlling for IQ, socioeconomic status, alcohol use, and smoking, the ADHD groups performed worse than comparison groups on verbal memory, processing speed, decision-making, working memory, and response inhibition.
No significant effects of adult cannabis use emerged on any cognitive measure. There were also no significant interactions between ADHD and cannabis use, meaning cannabis did not worsen cognitive deficits beyond what ADHD alone produced.
However, exploratory analyses suggested that individuals who began regular cannabis use before age 16 may have poorer executive functioning than those who started later.
Why it matters
This study challenges the assumption that cannabis use in adulthood necessarily adds to the cognitive impairments associated with ADHD. The finding that age of cannabis initiation may matter more than current use aligns with broader research on adolescent brain vulnerability.
The numbers in context
The study included 128 young adults (mean age 24.2 years). The ADHD group showed deficits across six cognitive domains compared to comparison participants. 27 individuals began regular cannabis use before age 16, and 32 began at age 16 or later.
How the study worked
This cross-sectional study compared 87 young adults with childhood ADHD diagnoses (42 cannabis users, 45 non-users) to 41 local comparison participants (20 cannabis users, 21 non-users) on a battery of neuropsychological tests. Cannabis use was defined as past-year monthly or more frequent use. Covariates included age, gender, IQ, socioeconomic status, and past-year alcohol and tobacco use.
What this study cannot tell us
The cross-sectional design cannot determine causation. The cannabis-using groups were relatively small, particularly for the exploratory age-of-onset analysis. Only past-year use was measured, not lifetime cumulative exposure. The study could not fully account for all potential confounds.
How to read the evidence
Well-controlled cross-sectional comparison with appropriate covariates, but limited by small subgroup sizes and inability to establish causation.
When this study was published
Published in 2013. The relationship between ADHD and cannabis continues to be studied.
The bigger picture
ADHD and cannabis use frequently co-occur, and a significantly greater proportion of the ADHD group began using cannabis before age 16. Understanding whether cannabis independently worsens ADHD-related cognitive problems is important for clinical guidance, and this study suggests the answer may depend more on when cannabis use begins than whether it continues in adulthood.
Questions still open
- Would longitudinal tracking show different results? Does the amount of cannabis used matter more than the binary of use vs. non-use? What mechanisms might explain the apparent vulnerability of the pre-16 brain to cannabis effects?
Common questions
Does cannabis make ADHD-related cognitive problems worse?
Does the age you start using cannabis matter for cognition?
Read the original research
Impact of ADHD and cannabis use on executive functioning in young adults.
Drug and alcohol dependence, 133(2), 607-14
Citation
Tamm, Leanne; Epstein, Jeffery N; Lisdahl, Krista M; Molina, Brooke; Tapert, Susan; Hinshaw, Stephen P; Arnold, L Eugene; Velanova, Katerina; Abikoff, Howard; Swanson, James M. (2013). Impact of ADHD and cannabis use on executive functioning in young adults.. Drug and alcohol dependence, 133(2), 607-14. https://doi.org/10.1016/j.drugalcdep.2013.08.001
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