CBD did not reduce THC side effects and actually increased THC blood levels and psychoactive effects in a clinical trial

Co-administration of 450 mg CBD with 9 mg THC increased "Feeling High" by 60.5%, more than doubled THC blood levels (AUC ratio 2.18), and increased the active metabolite 11-OH-THC levels (AUC ratio 1.89). Lower CBD doses (10 and 30 mg) also affected pharmacokinetics. CBD did not counteract psychomotor, cognitive, or autonomic effects of THC, and did not improve THC's analgesic properties.

Randomized, double-blind, placebo-controlled, five-way crossover trial in 37 healthy volunteers. Each participant received double-placebo, THC 9mg alone, or THC 9mg with CBD 10, 30, or 450 mg orally. Standardized test batteries for psychoactive and analgesic effects. Pharmacokinetic sampling.

This is among the most rigorous tests of the widely held assumption that CBD counteracts THC. The finding that CBD increases rather than decreases THC effects has major implications for cannabis product labeling, dosing guidelines, and the marketing of CBD-containing products as "safer."

CBD likely increases THC effects through pharmacokinetic interaction (inhibiting THC metabolism in the liver), not pharmacodynamic antagonism. This means CBD-containing cannabis products may actually be more potent, not less, challenging a widespread consumer assumption.

Oral administration only; inhaled cannabis may have different pharmacokinetic interactions. Single-dose study in healthy volunteers with no cannabis tolerance. THC dose (9 mg) is relatively low. Laboratory setting does not replicate real-world use conditions.