Single doses of both THC and cocaine reduced impulse control accuracy in heavy cannabis users, though cannabis also impaired motor function while cocaine improved it.
Read this if you want to understand how THC and cocaine each affect decision-making and impulse control in experienced users.
Both THC and cocaine reduced impulse control accuracy in heavy users
What the researchers found
In a study of 61 heavy cannabis users with cocaine use history, single doses of THC impaired both psychomotor function and impulse control accuracy. Cocaine had a different pattern: it improved psychomotor speed but still increased errors on impulse control tasks.
Both substances reduced the proficiency of impulse control, meaning participants made more errors even when they felt faster. The psychomotor impairments from THC appeared smaller in magnitude compared to those previously reported in occasional cannabis users, consistent with tolerance development.
The finding that both drugs decreased impulse control proficiency suggests that acute intoxication with either substance may increase the risk of impulsive decision-making, including the decision to use more drugs.
Why it matters
Cannabis and cocaine are among the most commonly used drugs in Europe, and they are frequently used together. Understanding how each substance independently affects impulse control in the same population of heavy users provides insight into patterns of continued use and potential relapse risk.
The numbers in context
61 heavy cannabis users participated. THC dose was weight-based. Cocaine dose was 300 mg. THC impaired psychomotor function and increased impulse errors. Cocaine improved psychomotor speed but also increased impulse errors.
How the study worked
Double-blind, placebo-controlled, three-way crossover study. Sixty-one heavy cannabis users with cocaine use history received single doses of cannabis (THC based on body weight), cocaine HCl (300 mg), and placebo in randomized order. Participants completed tests of impulse control and psychomotor function after each condition.
What this study cannot tell us
The study included only heavy cannabis users with cocaine experience, so results may not apply to occasional users or cannabis-only users. Single-dose administration may not reflect real-world polydrug use patterns. The crossover design assumed no carryover effects between conditions.
How to read the evidence
Well-designed placebo-controlled crossover trial, though limited to a specific population of heavy users with polysubstance history.
When this study was published
Published in 2013.
The bigger picture
The finding that both drugs impair impulse control accuracy raises an important point about the cycle of drug use: being under the influence of one substance may reduce the ability to resist using another. This has implications for understanding polysubstance use patterns.
Questions still open
- Does the combination of THC and cocaine together produce greater impulse control deficits than either alone? Do the tolerance effects on psychomotor impairment extend to impulse control as well? How do these acute effects influence real-world drug use decisions?
Common questions
Do heavy cannabis users develop tolerance to THC impairment?
Does cocaine improve or impair brain function?
Read the original research
Single doses of THC and cocaine decrease proficiency of impulse control in heavy cannabis users.
British journal of pharmacology, 170(7), 1410-20
Citation
van Wel, J H P; Kuypers, K P C; Theunissen, E L; Toennes, S W; Spronk, D B; Verkes, R J; Ramaekers, J G. (2013). Single doses of THC and cocaine decrease proficiency of impulse control in heavy cannabis users.. British journal of pharmacology, 170(7), 1410-20. https://doi.org/10.1111/bph.12425
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