The researchers found little objective evidence that cannabis benefits people with MS but, subjectively, a majority of patients felt cannabis improved some of their symptoms.
The results of the world's largest study to assess the medicinal potential of cannabinoids to treat MS patients are published in this week's edition of The Lancet.
The research team based at the Peninsula Medical School and the University of Plymouth was led by Dr. John Zajicek, Consultant Neurologist and Associate Medical Director of Research and Development at Plymouth Hospitals NHS Trust. The other principal investigator was Professor Alan Thompson, Consultant Neurologist at the National Hospital for Neurology and Neurosurgery, University College Hospitals, London. The trial that involved 33 neurology and rehabilitation centres across the UK was funded by the MRC and supported by the MS Society.
The three year trial of more than 600 patients from across the UK set out to look at whether cannabinoids can reduce muscle stiffness, known as spasticity, in the arms and legs of MS patients and to assess their general wellbeing in relation to other symptoms.
Participants in the trial were randomly assigned to oral capsules containing either cannabis extract, Tetrahydrocannabinol (THC, - an active compound found in cannabis), or a placebo and treated for 15 weeks. No patient was left without medication to manage their illness. The trial treatments were administered in addition to participants' own standard MS medication. The patients were not told which treatment they were taking.
The researchers found that when spasticity was assessed clinically using a well-established measure known as the Ashworth scale1 there was no overall detectable change in spasticity in the patients.
Four secondary measures were also used in the study: time to walk ten metres for mobile patients; a range of scales to assess disability and well-being; some measures of specific symptoms; and finally face-to face questions about the value of medication at the end of the study.
In face-to-face interviews, 576 patients provided answers to the end of study questions. Around two thirds of patients on the cannabis-based treatments said they felt their spasticity had improved, as did almost half of the patients taking a placebo, or dummy pill.
A benefit of cannabis-based medicine was also seen in results from the walking time. There was no benefit seen in any of the scales measuring general disability or wellbeing.
Patients were also asked to complete self assessment questionnaires about a range of symptoms associated with MS including irritability, depression, tiredness, spasticity, shake/tremor, pain, sleeplessness, spasms and lack of energy. Just over half the patients who completed the questionnaires on the cannabis-based treatments said spasticity had improved, but just over a quarter of these patients said they felt their symptoms had got worse. Overall, more patients taking active treatment said they experienced improvement in spasticity, pain, spasms and sleep compared to those taking placebo.
The researchers said that the results needed to be interpreted with caution as around three-quarters of patients in the active treatment group correctly guessed that they were taking active medication, compared to around half of the placebo group, who guessed they were not.2
Dr. Zajicek said: "The results of this study present an interesting and complex picture of the value of cannabis-derived medicines for treating MS. The primary aim of the trial was to measure, as objectively as possible, the actual physical changes in limb spasticity in MS patients, and we found no evidence of this.
"Although we based the study around spasticity, we also wanted to capture any treatment effects among the other important symptoms described by people with MS. When patients were asked to describe how they felt their symptoms, including spasticity, had been affected, the picture was very different. They felt some of the impact of their painful and distressing symptoms had been eased.
"We did see a high 'placebo effect' in this trial and it may be indicative of how much patients gain by taking part in clinical trials, irrespective of the treatment they are given.
"Patients experienced very few side-effects from the treatments and, given that how a patient feels is an important part of improving health, cannabis-based treatments may be of benefit to some patients."
Professor Colin Blakemore, Chief Executive of the Medical Research Council, said: "Science isn't always black and white and this work underlines the importance of funding large-scale clinical trials of possible treatments so the evidence can be weighed up.
"Clinical research is at the heart of the MRC's aim to improve health and we will continue to use clinical trials to put treatment theories to the test, across all areas of health."
1. The Ashworth scale is a score of spasticity. It is an assessment of biological impairment, rather than disability or handicap and is dependent upon the estimation of the physician or physiotherapist.
2. Patients' guesses were not confirmed to them. It was important to keep the trial 'blinded' to retain the integrity of the data, so for the duration of the trial patients were not told what treatments they were receiving.
3. The Medical Research Council (MRC) is a national organisation funded by the UK tax-payer. Its business is medical research aimed at improving human health; everyone stands to benefit from the outputs. The research it supports and the scientists it trains meet the needs of the health services, the pharmaceutical and other health-related industries and the academic world Web site at: http://www.
4. The MRC grant for the CAMS (Cannabinoids in MS) trial was awarded in December 1999.
5. Cannabinoids are natural chemicals found in cannabis, that all have a similar chemical structure and which have been shown to act on specific targets found in the body. The cannabis extract contains 60 different cannabinoids. THC is commonly believed to be the most active compound in cannabis.
6. It is estimated that around 85, 000 people in the UK have multiple sclerosis, the most common disabling neurological disease affecting young adults in the Western world.
7. The Lancet is an international general medical journal - http://www.
Source: Medical Research Council Media Release