CBD Increased THC's High and Blood Levels, While Caffeine Had Minimal Impact

Caffeine produced minimal changes in THC-induced subjective effects, performance, or metabolism, though signals for perceived driving impairment were observed. CBD, co-administered with THC and caffeine, increased abuse-liability outcomes (drug high, p=0.002), performance impairment, and plasma THC (p=0.004) and 11-OH-THC (p<0.001) concentrations compared to THC alone.

Double-blind, randomized, placebo-controlled, within-subject crossover study. 20 participants (10 men/10 women) completed outpatient sessions with oral THC (7.5 mg), caffeine (180 mg), and/or CBD (105 mg) in cumulative dosing design. Outcomes: subjective effects, simulated driving, plasma concentrations.

Cannabis products premixed with caffeine are increasingly common but have never been studied. The unexpected finding that CBD increases THC's effects and blood levels challenges the common belief that CBD moderates THC's impact.

The finding that CBD increases THC's high and blood levels has major implications for product labeling, dosing guidance, and the popular narrative that CBD 'balances out' THC. It also highlights the importance of considering full cannabinoid profiles in regulation.

Small sample (20). Oral administration only, not smoking or vaping. Specific doses may not represent commercial products. Single-session acute effects. Cannot determine chronic co-administration effects.