A two-year study says medical cannabis keeps working for arthritis pain — but 1 in 7 patients had a notable side effect

Researchers from Imperial College London, King's College London and several NHS trusts tracked 192 patients from the UK Medical Cannabis Registry who'd been prescribed cannabis-based medicinal products for pain tied to inflammatory arthritis, following them for up to 24 months. The study, published September 9 in Clinical Medicine Insights: Arthritis and Musculoskeletal Disorders, is observational — there's no placebo arm, so it can't rule out expectation effects — but it's a real longitudinal look at what happens to patients over time, not just a snapshot.

Using standard tools including the Brief Pain Inventory and the Short-Form McGill Pain Questionnaire, researchers found significant pain improvement at every single follow-up point from month 1 through month 24. Sleep quality and overall health-related quality of life improved and held across the full two years too; anxiety scores improved mainly in the first three months and were less consistent after that.

Twenty-seven of the 192 patients — about 14% — reported adverse events across the study, 296 in total: 43% mild, 45% moderate, and roughly 13% severe, though researchers noted none were life-threatening. That's a meaningful side-effect rate worth weighing against the pain and sleep gains, not a footnote to skip past.

Two years of sustained data beats another eight-week trial for answering the question patients actually care about — does this keep working, or fade out — and here the answer leans toward "keeps working." But without a control arm, this still isn't proof cannabis caused the improvement rather than correlating with it, and the real adverse-event rate is a legitimate reason for prescribers to keep monitoring rather than treat it as a settled, low-risk option.