In a controlled study, cocaine improved accuracy and speed on an impulse control task while cannabis impaired both, and their effects on brain electrical activity were mirror images of each other.
Read this if you want to understand exactly how cannabis affects impulse control compared to other substances.
Cannabis and cocaine had precisely opposite effects on impulse control accuracy, speed, and brain wave amplitude.
What the researchers found
In a double-blind, placebo-controlled crossover study, 38 healthy drug-using volunteers received cocaine, cannabis, and placebo in separate sessions and performed a Go/NoGo impulse control task.
Cocaine improved performance: faster reaction times, better accuracy, and increased prefrontal NoGo-P3 brain activity (reflecting enhanced evaluative processing). Cannabis produced the opposite: slower reactions, worse accuracy, and decreased NoGo-P3 amplitude.
Cannabis also reduced the parietal P3 wave, suggesting broader attention disruption beyond just impulse control. Cocaine did not affect this component, indicating its effects were more specific to response control.
Neither drug affected the N2 brain wave component, which reflects the earlier, pre-motor stage of response inhibition. This means both drugs acted on the evaluative stage (deciding whether the response was appropriate) rather than the initial detection stage.
Neither trait impulsivity nor novelty seeking moderated any drug effects.
Why it matters
This is one of the few controlled studies directly comparing how two commonly used drugs affect the same cognitive process in the same individuals. The finding that they have precisely opposite effects on impulse control, and that these effects are reflected in measurable brain activity, provides a clear neural picture of how these substances modify cognitive function.
The numbers in context
38 participants in a three-way crossover design. Cocaine: faster RTs, better accuracy, increased prefrontal NoGo-P3. Cannabis: slower RTs, worse accuracy, decreased prefrontal NoGo-P3 and parietal P3. Neither drug affected N2. Personality traits did not moderate effects.
How the study worked
Double-blind, placebo-controlled, randomized three-way crossover design. 38 healthy drug-using volunteers completed a Go/NoGo task after receiving cocaine, cannabis, or placebo in separate sessions. Event-related potentials (ERPs) were recorded via EEG. Trait impulsivity and novelty seeking were measured as potential moderators.
What this study cannot tell us
All participants were experienced drug users, so results may not generalize to drug-naive individuals. The study measured acute effects of single doses and does not address chronic use patterns. The crossover design controls for individual differences but cannot capture long-term neuroadaptations. Sample size was moderate.
How to read the evidence
Strong evidence from a well-designed double-blind, placebo-controlled, within-subject crossover study using both behavioral and neurophysiological measures.
When this study was published
Published in 2016. The acute cognitive effects of cannabis continue to be studied with advancing neuroimaging and EEG techniques.
The bigger picture
Understanding how different drugs affect impulse control has implications for driving safety, workplace performance, and treatment. The mirror-image effects of cocaine and cannabis on the same brain process illustrate why polysubstance use creates complex and potentially unpredictable cognitive states.
Questions still open
- What happens to impulse control when cocaine and cannabis are used simultaneously, as they frequently are? Would these effects be more or less pronounced in non-experienced users? Do the ERP changes predict real-world impulsive behavior like risky driving?
Common questions
Does cannabis affect impulse control?
Does personality predict how drugs affect you?
Read the original research
Acute effects of cocaine and cannabis on response inhibition in humans: an ERP investigation.
Addiction biology, 21(6), 1186-1198
Citation
Spronk, Desirée B; De Bruijn, Ellen R A; van Wel, Janelle H P; Ramaekers, Johannes G; Verkes, Robbert J. (2016). Acute effects of cocaine and cannabis on response inhibition in humans: an ERP investigation.. Addiction biology, 21(6), 1186-1198. https://doi.org/10.1111/adb.12274
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