The Landmark CAMS Trial: 667 MS Patients Test Cannabis for Spasticity | Research

The takeaway

The largest cannabis-MS trial found no improvement on the Ashworth spasticity scale, but patients reported significant improvements in spasticity and pain, and objective mobility measures improved.

Read this if you have MS and want to know about the largest clinical trial of cannabis for spasticity.

667 patients: Ashworth scale negative (p=0.40) but patient-reported spasticity improved (p=0.003)

What the researchers found

In this landmark trial of 667 MS patients across 33 UK centers, neither oral cannabis extract nor THC improved spasticity as measured by the Ashworth scale (primary outcome, p=0.40). However, patient-reported spasticity improvement was significantly better with both active treatments compared to placebo (p=0.003): 61% on cannabis extract, 60% on THC, and 46% on placebo reported improvement.

Objective mobility measures also improved in the treatment groups. The trial raised important questions about whether the Ashworth scale, a clinician-rated measure, adequately captured the spasticity improvements that patients experienced.

Why it matters

The CAMS study was the largest randomized trial of cannabis for MS at the time and remains one of the most important. The disconnect between negative objective spasticity results and positive patient-reported outcomes sparked a major debate about outcome measurement in spasticity research and whether clinician-rated scales adequately capture patient experience.

The numbers in context

667 patients enrolled, 630 treated, 611 followed for primary endpoint. Cannabis extract: n=211, THC: n=206, placebo: n=213. Primary outcome p=0.40 (not significant). Patient-reported improvement: 61% cannabis extract, 60% THC, 46% placebo (p=0.003). Trial duration: 15 weeks at 33 UK centers.

How the study worked

This was a randomized, placebo-controlled trial enrolling 667 patients with stable MS and muscle spasticity at 33 UK centers. Patients received oral cannabis extract (n=211), THC (n=206), or placebo (n=213) for 15 weeks. The primary outcome was change in Ashworth scale spasticity scores. Analysis was by intention to treat. Patient-reported outcomes and objective mobility measures were secondary endpoints.

What this study cannot tell us

The primary outcome was negative, and the study technically failed to demonstrate efficacy. Some unmasking occurred (patients could tell they were on active treatment), potentially biasing patient-reported outcomes. The 15-week duration may have been insufficient for full therapeutic effect. Oral dosing required dose titration that some patients may not have optimized.

How to read the evidence

This is a large, multicenter, randomized, placebo-controlled trial with 667 patients, providing strong evidence despite the mixed results.

When this study was published

Published in 2003. This landmark trial influenced subsequent research and the eventual approval of Sativex for MS spasticity.

The bigger picture

Despite the negative primary outcome, the CAMS study contributed to the eventual approval of Sativex for MS spasticity, partly because it demonstrated meaningful patient-reported benefits. The study also led to a follow-up trial (MUSEC) that used patient-reported outcomes as the primary measure and found positive results. The Ashworth scale has been increasingly questioned as a spasticity measure since this trial.

Questions still open

Does the Ashworth scale adequately measure spasticity as experienced by patients? Should patient-reported outcomes be primary endpoints in spasticity trials? Did the follow-up MUSEC trial resolve the ambiguity?

Common questions

Did cannabis help with MS spasticity in this trial?

It depends on how you measure it. The clinician-rated Ashworth scale showed no improvement, but patients themselves reported significantly less spasticity (61% improved on cannabis vs 46% on placebo). This discrepancy raised important questions about how spasticity should be measured.

Why do patients and doctors disagree about whether spasticity improved?

The Ashworth scale measures muscle stiffness during passive limb movement by a clinician, which may not capture the dynamic spasticity that patients experience during daily activities. Patients may feel genuinely less stiff and move more easily even if the Ashworth measurement does not change.

Read the original research

Cannabinoids for treatment of spasticity and other symptoms related to multiple sclerosis (CAMS study): multicentre randomised placebo-controlled trial.

Lancet (London, England), 362(9395), 1517-26

View on PubMed ↗

Citation

Zajicek, John; Fox, Patrick; Sanders, Hilary; Wright, David; Vickery, Jane; Nunn, Andrew; Thompson, Alan. (2003). Cannabinoids for treatment of spasticity and other symptoms related to multiple sclerosis (CAMS study): multicentre randomised placebo-controlled trial.. Lancet (London, England), 362(9395), 1517-26.