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[2008 updates are highlighted in red]
| Description: |
For years, it has been claimed that cannabis, also known as marijuana, is an effective treatment for MS (see also “Spasticity” section of Chapter 4). Cannabis, which is illegal in many countries, contains compounds known as cannabinoids. These compounds, which include tetrahydrocannabinol (THC), produce specific biochemical effects in the body. Cannabis may be smoked or ingested. There are prescription medications that contain cannabinoids. In the United States, THC is available as dronabinol (Marinol®). In Europe, Canada, and Australia, a synthetic form of THC is available as nabilone (Cesamet®). |
| Rationale: |
Cannabinoids exert several biological effects that, on a theoretical basis, could be therapeutic for MS. First, they bind to proteins in the central nervous system (CB1 receptors) that suppress excessive nerve cell activity. This could, on a theoretical basis, decrease some MS symptoms such as pain and muscle stiffness (spasticity). Also, cannabinoids bind to another type of protein on immune cells (CB2 receptors) and mildly suppress the immune system. It is possible that cannabinoids are able to slow down the disease process in MS through this mechanism. Finally, cannabinoids may protect against nerve cell injury by decreasing the damage caused by free radicals and “excitotoxicity,” an injurious form of excitatory nerve cell activity. |
| Evaluation: |
Studies of the effects of cannabis on MS and experimental allergic encephalomyelitis (EAE), the animal model of MS, are limited and inconclusive. In EAE, some symptoms, including spasticity and tremor, are improved with cannabinoid treatment. In addition, high doses of cannabinoids decrease the overall severity of EAE. There are mixed results in studies of the actual disease in humans. In several surveys of people with MS who have smoked cannabis, symptoms commonly reported to be improved include pain, spasticity, depression, anxiety, and sleeping difficulties. Importantly, surveys such as this are not rigorous enough to provide definitive evidence for effectiveness. Actual clinical studies of the effects of smoked or oral cannabis on MS symptoms are of variable quality. Some, but not all, of these studies have found improvement in spasticity. A 1999 review by the National Academy of Sciences/Institute of Medicine (NAS/ IOM) stated that there was suggestive evidence that smoked and oral cannabis may alleviate MS-related spasticity. In 2003, the results of the first large formal clinical trial of an extract of cannabis and oral THC on MS symptoms were reported. For a variety of MS symptoms, there was no therapeutic effect as determined by objective tests based on clinical exams. However, subjective benefits, as reported by people in the study, were found for spasticity, pain, and sleep quality. In a 12-month follow-up to this study, THC showed a small treatment effect on muscle spasticity, and there was a suggestion of a therapeutic effect on disability, especially in the THC-treated group. Studies of an orally administered form of cannabis have shown beneficial effects on multiple MS symptoms, including pain, spasticity, and sleeping difficulties. In the United Kingdom, the “CUPID” study (cannabinoid use in progressive inflammatory brain disease) is evaluating the effects of oral THC on approximately 500 people with progressive MS. The effects of cannabis on the immune system and on disease activity in MS are not clear. Contrary to what one might expect, one study found that cannabinoids actually produced immune-stimulating effects. |
| Risks: |
There are significant risks associated with smoking cannabis, including nausea, vomiting, sedation, increased risk of seizures, and poor pregnancy outcomes. Driving may be impaired for up to 8 hours after smoking cannabis. High doses of cannabis may impair heart function, decrease reaction time, and produce coordination and visual difficulties. Chronic cannabis use may cause heart attacks, impair lung function, cause dependence and apathy, and increase the risk of cancer of the lung, head, and neck. |
| Costs: |
Smoked cannabis and prescription medications containing cannabinoids are of low-moderate cost. |
| Committee opinion: |
In the opinion of the Committee, additional research is needed to determine if cannabis is safe or effective in MS. Some experimental and clinical studies suggest that cannabis may alleviate some MS symptoms and may decrease the severity of the disease. However, there is limited evidence for a therapeutic effect, there are significant risks associated with cannabis, and cannabis is illegal in many countries. |
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