Under the acute influence of THC, healthy volunteers showed a heightened tendency to form false memories compared to those given a placebo. In a double-blind, randomized trial, 64 participants completed memory tasks—including associative word lists and two virtual-reality misinformation scenarios—immediately while intoxicated and again one week later while sober. Intoxicated individuals exhibited a stronger false-recognition bias, especially when test items were weakly associated with studied material, and were more susceptible to misinformation in eyewitness and perpetrator scenarios. These false-memory effects were largely confined to the acute intoxication phase. The findings suggest that cannabis increases false-memory proneness and have practical implications for police interviews with suspects and eyewitnesses.
Cannabis intoxication and a history of regular cannabis use are linked to a more liberal response criterion in memory tasks, leading to higher false recognition of unrelated items. In a field study using the Deese/Roediger-McDermott (DRM) paradigm, regular cannabis consumers who were acutely intoxicated (n = 53), regular cannabis consumers who were sober (n = 50), and cannabis-naïve controls (n = 53) completed a memory test. False memory rates for critical lures did not statistically differ between groups, but both intoxicated and sober cannabis consumers falsely recognized more unrelated items than controls. Cannabis-naïve individuals showed higher memory accuracy compared with the intoxicated group.
A double-blind, placebo-controlled trial with 60 healthy volunteers who had previously used MDMA examined the drug's effects on false memory. Participants received 75 mg of MDMA or a placebo and were tested using a word list task and two misinformation tasks involving a virtual reality crime scene. Memory was tested immediately and one week later. MDMA caused small impairments in true memory on the word list task at both time points. It increased false memory for related but non-critical lures immediately but decreased false memory for critical lures after a week. Episodic memory in the misinformation tasks was not consistently affected. The findings suggest no heightened vulnerability to external suggestion during MDMA intoxication.