spasms often affect the legs and can disrupt sleep. Most people with MS experience intermittent “attacks” of spasticity that become increasingly disabling the longer they have the disease. In the worst cases, patients become partially or even completely paralyzed.

The drugs most commonly prescribed to treat the symptoms of MS include baclofen (Lioresal) and tizanidine (Zanaflex) which relieve both spasticity and muscle spasms but often only partially and sometimes not at all. Both are sedatives, so they cause drowsiness; additional side effects include dry mouth and muscle weakness. The latter is especially problematic for people with MS, whose muscles get weaker as the disease progresses.

Both marijuana and THC have been tested for their ability to relieve spasticity in small but rigorous clinical studies. One double-blind experiment (see Introduction to Part II for an explanation of double-blind methods) included both MS patients and unaffected individuals.3 Before and after smoking a single marijuana cigarette that contained approximately 15 milligrams of THC—enough to make most people feel “high” and to impair their motor control—patients were videotaped as they stood on a platform that slid back and forth at unpredictable times. The researchers then measured participants ' shoulder movements as an index for how well they kept their balance.

Participants with MS often thought that their symptoms had improved after smoking marijuana. But while their spasticity may indeed have decreased (it was not measured), their posture and balance were actually impaired; this was also the case with the 10 participants who did not have MS. The MS patients had greater difficulty maintaining their balance before smoking and were more negatively affected by marijuana than the healthy participants.

While the fact that every MS patient in the previous study experienced relief is intriguing, it does not constitute strong evidence that marijuana relieves spasticity because marijuana-induced euphoria or pain relief might decrease patients' perceptions of muscle stiffness or spasticity. The same is true of respondents to the surveys described earlier. Moreover, surveys cannot measure the degree to which respondents feel better simply because they expect to do so. Such placebo effects are signifi-



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