Study: No Measurable Next-Day Cognitive Effects Following Cannabis Use
- Research published in Drug and Alcohol Dependence Reports found no significant cognitive performance differences between cannabis consumers tested 12–15 hours after use and non-consumers.
- The study aligns with previous findings showing little evidence of next-day impairment from cannabis, including effects on driving ability.
- Despite no cognitive impairment, cannabis users may still test positive for trace THC levels in blood for days and for inactive metabolites in urine for weeks after use.
- NORML emphasizes that current drug testing policies are outdated and unfair, advocating for performance-based workplace testing instead of detection of THC presence to assess impairment accurately.
Those who consume cannabis the previous evening perform no differently than non-consumers on cognitive measures, according to data published in the journal Drug and Alcohol Dependence Reports.
Canadian investigators assessed cognitive performance in a cohort of cannabis consumers and similarly matched abstainers. Consumers smoked cannabis 12 to 15 hours prior to testing.
Researchers reported “no significant group differences” on any cognitive measures.
They concluded: “Contrary to our hypothesis, we found no cognitive performance differences between the cannabis group (tested 12–15 h after last use) and controls. This aligns with a systematic review reporting little evidence of next-day performance effects of cannabis exposure.”
The study’s results are consistent with those of others finding no next-day driving impairment in consumers who used cannabis the night before. Nonetheless, some consumers may continue to test positive for trace levels of THC in their blood for several days. They may test positive for the presence of inert THC metabolites in their urine for several weeks.
Commenting on the findings, NORML’s Deputy Director said: “These results have significant policy implications, particularly with respect to the use of traditional workplace drug testing. Far too often, these tests sanction workers for off-duty behavior from days earlier that poses no occupational safety threat. THC per se standards are similarly problematic and risk punishing drivers who are no longer impaired. It is high-time to abandon these discriminatory methods in favor of performance testing and fit-for-duty testing, which employ measures to assess whether someone is currently under the influence, whether it be from marijuana on anything else.”
Full text of the study, “Cognitive performance and subjective effects the morning after last use of smoked cannabis by adults who use cannabis frequently: An observational study,” appears in Drug and Alcohol Dependence Reports. Additional information is available from the NORML Fact Sheet, ‘Marijuana and Cognitive Performance.’