Cannabis Impairs Nearly Every Type of Memory, Not Just Verbal Recall

Compared to placebo, cannabis increased false memory susceptibility and impaired verbal memory (immediate, delayed, working), visuospatial memory (immediate, delayed), event-cued prospective memory, source memory, and temporal order memory. No significant differences were found between 20mg and 40mg THC doses.

Randomized, double-blind, placebo-controlled study with 120 cannabis-using participants assigned to vaporize flower containing 0mg (placebo), 20mg, or 40mg THC. Comprehensive battery of 13 memory tests spanning verbal, visuospatial, prospective, source, false, episodic, and temporal order memory domains.

Most cannabis memory research focused only on verbal recall. This study reveals that cannabis broadly impairs nearly all memory types, including 'everyday' memory like remembering to take medication or recalling the order of events — with real implications for daily functioning.

The lack of dose-response (20mg and 40mg THC produced similar impairment) suggests a ceiling effect — once a moderate threshold is reached, more THC doesn't worsen memory further. The broad impairment pattern challenges the idea that cannabis only affects specific memory types.

Participants were existing cannabis users (tolerance may affect results). Single acute administration. Flower vaporization only — edibles may differ. Lab setting may not fully reflect real-world use. Young adult sample may not generalize to all ages.