CBD Added to Paracetamol Did Not Improve Knee Osteoarthritis Pain Beyond Placebo

Pain improved in both groups of a knee-osteoarthritis trial, but adding CBD did not provide a significant advantage over placebo. The CBD group also had more adverse events, making within-group improvement an incomplete description of the findings.

An add-on trial rather than CBD alone

Eighty-six participants were randomized to 600 mg oral CBD daily or placebo for eight weeks. All continued paracetamol at 3 g per day. The primary outcome was change in the pain subscale of the WOMAC osteoarthritis assessment.

Fifty-eight participants completed the trial. The randomized population and the completer population are therefore different denominators. Attrition and the trial’s intention-to-treat approach matter when interpreting the reported averages.

Improvement was almost the same with placebo

Mean pain-score reduction was 2.5 points with CBD and 2.4 with placebo, with no significant treatment difference (p = 0.80). Secondary functional outcomes likewise did not establish superiority of CBD.

Adverse events were more frequent with CBD, and rises in measured liver enzymes were more common. The reported totals of adverse events count events rather than independent people; one participant can contribute more than one event. No serious adverse event was observed in this relatively small trial.

The treatment context limits extrapolation

The findings concern chronic knee osteoarthritis and CBD added to ongoing paracetamol. They do not establish how CBD alone would compare with no treatment, nor how another pain condition, dose or formulation would respond.

The randomized contrast is the relevant evidence for an added analgesic benefit. Improvement from baseline, animal anti-inflammatory findings and a plausible biological mechanism cannot replace that comparison. This study supports a null add-on efficacy conclusion under its conditions, alongside a genuine tolerability signal.

Related: Why treatment outcomes require attention to study design.

Primary research

Oral cannabidiol (CBD) as add-on to paracetamol for painful chronic osteoarthritis of the knee: a randomized, double-blind, placebo-controlled clinical trial. The Lancet Regional Health – Europe (2023).