Long-term observational studies of cannabis for chronic pain show modest benefits but very low evidence quality | Research

The takeaway

A meta-analysis of six long-term observational studies found cannabis-based medicines produced modest pain reduction and some improvement in sleep for chronic non-cancer pain, but evidence quality was very low and nearly half of patients dropped out.

Patients considering long-term cannabis for pain, clinicians, and health policymakers evaluating evidence for medical cannabis.

21% of patients achieved ≥50% pain relief over 26-52 weeks

What the researchers found

Mean pain reduction was 1.75 points on a 0-10 scale (95% CI 0.72-2.78). About 20.8% of patients reported ≥50% pain relief. Sleep improvements were moderate in effect size, while depression and anxiety improvements were small. Only 53.3% of patients completed the studies, with 6.8% dropping out due to adverse events.

Why it matters

While RCTs of cannabis for pain are typically short-term, these longer observational studies (26-52 weeks) provide a more realistic picture of sustained use, including the concerning finding that nearly half of patients discontinue treatment.

The numbers in context

6 studies, 2,686 participants, 26-52 weeks duration. Pain reduction: 1.75/10. ≥50% relief: 20.8%. Study completion: 53.3%. Dropout from adverse events: 6.8%. Serious adverse events: 3.0%. Deaths: 0.3%.

How the study worked

Systematic review and meta-analysis of prospective observational studies with ≥26 weeks duration. Six studies with 2,686 participants were included. CENTRAL, EMBASE, and MEDLINE searched through December 2021. Random effects models used.

What this study cannot tell us

Very low certainty of evidence for all outcomes. Observational design without control groups. High dropout rates complicate interpretation. Heterogeneous pain conditions included. No standardized cannabis products across studies.

How to read the evidence

Systematic review and meta-analysis, but all included evidence was rated very low quality.

When this study was published

Published in 2022 with studies searched through December 2021.

The bigger picture

The gap between enthusiasm for cannabis as a pain treatment and the actual evidence base remains wide. These long-term data suggest that while some patients benefit meaningfully, most do not achieve large improvements and many stop treatment.

Questions still open

Why do nearly half of patients drop out? Are there identifiable subgroups who respond well to long-term cannabis therapy? Would standardized products and doses produce better outcomes?

Common questions

How much pain relief did cannabis provide on average?

Average pain reduction was 1.75 points on a 0-10 scale. About 1 in 5 patients (20.8%) achieved at least 50% pain relief, which is considered a clinically meaningful response.

How many patients continued treatment long-term?

Only 53.3% of patients completed the studies (26-52 weeks). About 6.8% dropped out specifically due to adverse events, with the rest discontinuing for other reasons.

Read the original research

Long-term observational studies with cannabis-based medicines for chronic non-cancer pain: A systematic review and meta-analysis of effectiveness and safety.

European journal of pain (London, England), 26(6), 1221-1233

View on PubMed ↗Publisher’s paper ↗

Citation

Bialas, Patric; Fitzcharles, Mary-Ann; Klose, Petra; Häuser, Winfried. (2022). Long-term observational studies with cannabis-based medicines for chronic non-cancer pain: A systematic review and meta-analysis of effectiveness and safety.. European journal of pain (London, England), 26(6), 1221-1233. https://doi.org/10.1002/ejp.1957