Cannabis and Physical Performance at Twelve Hours: Why the Result Is Not a Universal Work Rule
A study observed selected physical-performance changes up to twelve hours after cannabis smoking. Its design does not establish that everyone remains impaired for twelve hours or that everyone is safe immediately afterward.
Exposure was not randomly assigned
The study included 28 adults: fifteen in an experimental group and thirteen controls. Frequent users were deliberately assigned to receive cannabis, rather than randomized to exposure. Cannabis-use history differed significantly between the groups.
Participants performed tests before and after smoking, with follow-up at one, six and twelve hours. The outcomes included maximal force, rapid force development, endurance, force control and balance. They were occupationally relevant tasks, not measurements of actual workplace accidents.
The late effects were task-specific
Selected rapid-force measures were reduced at later assessments, and endurance at a submaximal force target was shorter at twelve hours in the experimental group relative to controls. Maximum voluntary force did not show a corresponding overall effect.
Subjective intoxication was minimal at twelve hours. Thus, feeling nearly sober did not establish normal performance on every tested function. Conversely, changes in selected functions did not show that all strength or balance outcomes deteriorated.
Use history complicates causation
Because habitual use helped determine group assignment, acute drug effects cannot be completely separated from other group differences or longer-term adaptation. Repeated measurements help describe change but do not transform the design into a randomized trial.
The sample was small and used a single product and route. The investigators did not establish an individual concentration threshold linked to the late task findings.
Applying the evidence carefully
The authors’ precautionary return-to-task advice should be distinguished from a validated universal clearance interval. No testing beyond twelve hours established exactly when each participant’s affected function recovered.
For an occupational opinion, specify the task, exposure history and comparison being used. The study supports caution about relying on subjective recovery alone, while leaving substantial uncertainty about an individual’s performance and the appropriate interval for a different job, product or dose.
For context, see our discussion of THC concentrations and the separate question of impairment.
Primary research
Waseem Abu-Ashour and colleagues. Physical Performance Impairment with Cannabis Consumption in Adults Over 12 Hours. Journal of Drug Education (2026). DOI: 10.1177/00472379261433203.
