Cannabis Use Not Linked to Cognitive Decline or Dementia Risk in Older Adults

In the UK Biobank, cannabis users performed modestly better on some baseline cognitive tests but showed no difference in longitudinal cognitive change. In the Million Veteran Program, cannabis use disorder was not significantly associated with dementia (HR=1.11, 95% CI=0.97-1.26, p=0.12). Mendelian randomization found no causal relationship in either direction.

Observational analyses in UK Biobank (up to 79,573 participants, cross-sectional and longitudinal cognitive testing) and US Million Veteran Program (12,222 with cannabis use disorder, Cox proportional hazards for dementia), plus bidirectional two-sample Mendelian randomization.

As cannabis use among older adults surges, many worry about cognitive effects — this large-scale evidence from two major cohorts and genetic analyses provides reassurance that cannabis use doesn't appear to accelerate cognitive aging.

This study shifts the narrative from assumed cognitive harm to evidence of no significant effect — but importantly, safety at higher doses or with prolonged heavy use remains uncertain.

Lifetime use measure doesn't capture current heavy use; UK Biobank may underrepresent heavy users; healthy volunteer bias; MR instruments may have limited power; cannot rule out effects at very high consumption levels; cannabis use disorder is extreme end of spectrum.