Psychoactive drugs and false memory: comparison of dextroamphetamine and delta-9-tetrahydrocannabinol on false recognition

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.

Study at a glance

Abstract

Rationale Several psychoactive drugs are known to influence episodic memory. However, these drugs’ effects on false memory, or the tendency to incorrectly remember nonstudied information, remain poorly understood. Objectives Here, we examined the effects of two commonly used psychoactive drugs, one with memory-enhancing properties (dextroamphetamine; AMP), and another with memory-impairing properties (Δ^9-tetrahydrocannabinol; THC), on false memory using the Deese/Roediger–McDermott (DRM) illusion. Methods Two parallel studies were conducted in which healthy volunteers received either AMP (0, 10, and 20 mg) or THC (0, 7.5, and 15 mg) in within-subjects, randomized, double-blind designs. Participants studied DRM word lists under the influence of the drugs, and their recognition memory for the studied words was tested 2 days later, under sober conditions. Results As expected, AMP increased memory of studied words relative to placebo, and THC reduced memory of studied words. Although neither drug significantly affected false memory relative to placebo, AMP increased false memory relative to THC. Across participants, both drugs’ effects on true memory were positively correlated with their effects on false memory. Conclusions Our results indicate that AMP and THC have opposing effects on true memory, and these effects appear to correspond to similar, albeit more subtle, effects on false memory. These findings are consistent with previous research using the DRM illusion and provide further evidence that psychoactive drugs can affect the encoding processes that ultimately result in the creation of false memories.