The Landmark CAMS Trial: 667 MS Patients Test Cannabis for Spasticity
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- 667 patients: Ashworth scale negative (p=0.40) but patient-reported spasticity improved (p=0.003)
- Evidence Grade:
- This is a large, multicenter, randomized, placebo-controlled trial with 667 patients, providing strong evidence despite the mixed results.
- Study Age:
- Published in 2003. This landmark trial influenced subsequent research and the eventual approval of Sativex for MS spasticity.
- Original Title:
- Cannabinoids for treatment of spasticity and other symptoms related to multiple sclerosis (CAMS study): multicentre randomised placebo-controlled trial.
- Published In:
- Lancet (London, England), 362(9395), 1517-26 (2003)
- Authors:
- Zajicek, John, Fox, Patrick, Sanders, Hilary, Wright, David, Vickery, Jane, Nunn, Andrew, Thompson, Alan
- Database ID:
- RTHC-00153
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked 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.
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Cite This Study
https://rethinkthc.com/research/RTHC-00153APA
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.
MLA
Zajicek, John, et al. "Cannabinoids for treatment of spasticity and other symptoms related to multiple sclerosis (CAMS study): multicentre randomised placebo-controlled trial.." Lancet (London, 2003.
RethinkTHC
RethinkTHC Research Database. "Cannabinoids for treatment of spasticity and other symptoms ..." RTHC-00153. Retrieved from https://rethinkthc.com/research/zajicek-2003-cannabinoids-for-treatment-of
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.