Acute oral doses of Δ⁹-tetrahydrocannabinol (THC) impair recognition of fearful and angry facial expressions but have only marginal effects on recognition of sadness and happiness. THC does not consistently alter ratings of emotional scenes, nor does its effect on emotional evaluation relate to its mood-altering properties. The findings indicate that THC specifically reduces perception of facial threat without positively biasing the evaluation of emotional stimuli more broadly.
Amphetamine (AMP) improves true memory for studied words, while THC impairs it, but neither drug significantly changes the tendency to falsely remember nonstudied words compared to placebo. Across participants, the drugs' effects on true memory correlated positively with their effects on false memory, suggesting that encoding processes influenced by these drugs similarly affect both accurate and false recollection. These results come from two within-subjects, double-blind experiments using the Deese/Roediger–McDermott illusion to test recognition memory two days after drug administration.