cant; for example, in controlled trials of pain medications, as many as 30 percent of the participants who received a placebo reported feeling relief. This does not mean that placebo effects are not “real.” It is possible that the psychological effects of taking a placebo drug cause physiological changes in the brain. But it does mean that the effects are not directly due to the medication being tested.
THC's effects on spasticity were tested in three separate clinical studies, which together enrolled a total of 30 MS patients.4 All three were open trials in which participants knew they would be receiving THC. Perhaps not surprisingly, most of the patients —or in one case the investigators who examined them—reported that treatment with THC improved their symptoms (see Figure 7.1). The drug was not effective for all patients, however, and frequently caused unpleasant side effects.
Objective measurements of patients' symptoms in these studies were often at odds with their subjective reports. In one study researchers measured muscle tremor with a mechanical device, which showed detectable change in only two of eight patients, seven of whom had reported improved symptoms.5 In another study standardized physician's measures showed that treatment with THC had not produced any changes in spasticity despite reports of reduced spasticity by 11 of 13 patients. 6 It may be that the measuring techniques used in both studies were not sensitive enough to detect subtle improvements. It is also possible that patients' reports of symptom improvement were influenced by placebo effects or by effects of THC, such as anxiety reduction, that are only indirectly related to spasticity. Neither possibility can be ruled out due to the small size of these studies.
In addition to these experiments on THC, a single patient who tested the THC analog nabilone—a synthetic compound that activates the same cellular receptors as THC—also reported an improvement in spasticity as well as in other MS symptoms (see Figure 7.2).7
These clinical results are considerably less dramatic than survey and anecdotal reports of marijuana's effectiveness in relieving muscle spasms. It is possible, however, that a series of larger, better-designed clinical trials would produce stronger evidence in favor of marijuana-based medicines for MS. At this writing