Understanding how cannabis and alcohol interact when consumed together has become increasingly urgent as both substances gain wider social acceptance and legal availability. This controlled laboratory study provides the first rigorous evidence of how combining edible cannabis products with alcohol affects critical safety measures like driving ability and field sobriety performance.
Researchers at Johns Hopkins conducted a sophisticated crossover trial with 25 healthy adults, testing combinations of THC edibles (10mg or 25mg) with varying alcohol levels (breath alcohol concentrations of 0.05% and 0.08%). Participants completed simulated driving tasks and standardized field sobriety tests across seven different sessions. The combination consistently produced more severe impairment than either substance alone, with the global drive score showing significant deterioration when both substances were present. Blood cannabinoid measurements confirmed that alcohol did not alter THC absorption patterns, indicating the interaction occurs at the level of psychomotor and cognitive function rather than metabolism.
This finding challenges the common assumption that low-dose combinations might be relatively safe. The study design represents a gold standard for impairment research, using double-blind protocols and within-participant comparisons that eliminate individual variation confounds. However, the laboratory setting and relatively small sample limit real-world applicability. The implications extend beyond traffic safety to workplace performance and daily activities requiring coordination. As cannabis legalization expands and social co-use becomes more normalized, these data suggest that current impairment thresholds developed for single substances may be inadequate for detecting combination effects, potentially requiring updated safety protocols and legal frameworks.