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

The takeaway

Across two large cohorts totaling over 250,000 participants, cannabis use was not associated with faster cognitive decline or increased dementia risk, with Mendelian randomization analyses finding no causal relationship.

Older adults using or considering cannabis, geriatricians, neurologists, dementia researchers, and policy makers assessing cannabis risks for aging populations.

What the researchers found

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.

Why it matters

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.

The numbers in context

UKB: up to 79,573 participants; MVP: 12,222 with cannabis use disorder vs controls; cannabis users slightly better on numeric memory (β=0.07) and fluid intelligence (β=0.12); no longitudinal difference; dementia HR=1.11 (NS); MR: no causal evidence

How the study worked

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.

What this study cannot tell us

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.

How to read the evidence

Convergent evidence from two large cohorts, multiple cognitive domains, longitudinal follow-up, and Mendelian randomization provides strong evidence for the null finding.

When this study was published

Published 2026 in BMJ Mental Health; uses UK Biobank and MVP data.

The bigger picture

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.

Questions still open

Would heavy daily use over decades show different results? Does the type or potency of cannabis matter for cognitive aging? Could cannabis actually be neuroprotective, or is the modest cognitive advantage due to confounding?

Common questions

Does cannabis cause dementia?

This large-scale study found no evidence that cannabis use increases dementia risk or accelerates cognitive decline in older adults, using both observational data from 250,000+ people and genetic analyses to test for causal relationships.

Is cannabis safe for older adults' brain health?

This study found no harmful cognitive effects from cannabis use in older adults, but couldn't fully assess heavy long-term use. Clinicians should still discuss cannabis use with older patients given potential interactions with medications.

Read the original research

Cannabis use, cognitive function and dementia risk in older adults: observational and genetic analyses.

BMJ mental health, 29(1)

View on PubMed ↗Publisher’s paper ↗

Citation

Ishrat, Saba; Levey, Daniel F; Gelernter, Joel; Ebmeier, Klaus P; Topiwala, Anya. (2026). Cannabis use, cognitive function and dementia risk in older adults: observational and genetic analyses.. BMJ mental health, 29(1). https://doi.org/10.1136/bmjment-2025-302290