Most Evidence Suggests Medical Cannabis Has Minor Effects on Thinking Skills | Research

The takeaway

A systematic review of 23 studies found that the majority of high-quality evidence suggests medical cannabis has minor negative effects on cognition at low to moderate THC doses, though long-term use may still pose risks.

Medical cannabis patients and clinicians concerned about cognitive side effects

23 studies, 917 participants

What the researchers found

Of 23 included studies (917 total participants), 15 found non-significant effects on cognition, 6 found impairments, 1 found improvement, and 1 found improvement after withdrawal. In studies that did find significant impairment, test scores remained within normal ranges or below clinical impairment thresholds.

Why it matters

Cognitive side effects are a common concern for patients considering medical cannabis. This review provides reassurance that at therapeutic doses, cognitive impairment appears minor, while also flagging that long-term use remains an open question.

The numbers in context

23 studies included; 917 total participants; 15 studies found non-significant cognitive effects; 6 found impairments; 8 used Sativex; 13 had cognition as primary outcome

How the study worked

Systematic review searching EMBASE, PsycINFO, PubMed, and Scopus. Included studies had to use cannabis-based medicines in controlled settings, measure cognition with recognized tests, and use within-subjects designs. Excluded studies on abuse, abstinence, severe neurodegeneration, and cancer pain. Two independent researchers conducted screening and risk of bias assessment.

What this study cannot tell us

Large heterogeneity across studies in terms of cannabis products, doses, cognitive measures, and patient populations. Most studies used relatively low THC doses. Limited evidence on long-term cognitive effects of medical cannabis use.

How to read the evidence

Systematic review with rigorous methods, but underlying studies had large heterogeneity and methodological limitations

When this study was published

2022 study

The bigger picture

As medical cannabis prescriptions grow worldwide, understanding cognitive trade-offs is essential for informed treatment decisions. This review suggests the cognitive cost may be lower than many patients and clinicians fear, at least in the short term.

Questions still open

At what THC dose threshold does cognitive impairment become clinically meaningful? Does long-term medical cannabis use lead to cumulative cognitive effects? Are certain cognitive domains more vulnerable than others?

Common questions

Does medical cannabis make it hard to think clearly?

Most studies in this review found no significant cognitive effects at low to moderate THC doses. When impairment was detected, scores still fell within normal ranges.

Is long-term medical cannabis use safe for cognition?

This review could not definitively answer that question. While short-term effects appear minor, the authors note that long-term use may still adversely affect cognitive functioning.

Read the original research

The effect of medical cannabis on cognitive functions: a systematic review.

Systematic reviews, 11(1), 210

View on PubMed ↗Publisher’s paper ↗

Citation

Wieghorst, Anders; Roessler, Kirsten Kaya; Hendricks, Oliver; Andersen, Tonny Elmose. (2022). The effect of medical cannabis on cognitive functions: a systematic review.. Systematic reviews, 11(1), 210. https://doi.org/10.1186/s13643-022-02073-5