Animal research, too, suggests that marijuana calms muscle spasticity. Spasms are thought to originate in areas of the brain that control movement, including several sites with abundant cannabinoid receptors. In one experiment, researchers found that rodents became more animated under the influence of small amounts of cannabinoids but less active when they received larger doses. Many marijuana users also note that the drug affects movement, making their bodies sway and their hands unsteady. The exact mechanism(s) by which cannabinoids exert these effects remains unknown.
Despite these suggestive findings and the depth of anecdotal evidence, marijuana's antispasmodic properties remain largely untested in the clinic. The few existing reports are extremely limited in scope; for example, none of the studies discussed in this chapter included more than 13 patients, and some were conducted on a single patient. Also, in several cases the patients' subjective evaluations of improvement contrasted with objective measures of their physical performance. Still, the lack of good universally effective medicine for muscle spasticity is a compelling reason to continue exploring cannabinoid drugs in the clinic.
Multiple sclerosis (or MS) is a progressive disease of the nervous system with no known cure. It appears to result from a malfunction of the immune system, which inflames nerves in the brain, brain stem, and spinal cord. Specifically, the disease destroys the protective coating called myelin that sheaths the neural fibers like insulation on electrical wire. Without an intact myelin layer, nerve cells lose some or all of their ability to transmit impulses. This situation produces an array of symptoms, including fatigue, depression, vertigo, blindness, incontinence, and loss of voluntary muscle control, as well as muscle spasticity. MS is characterized by scarring—“sclerosis ”—that occurs in the white matter of the central nervous system after nerves and myelin are lost.
Approximately 90 percent of MS patients develop spasticity. Some people experience this condition merely as muscle stiffness; others endure constant ache, cramps, or involuntary muscle contractions (spasms) that are both painful and debilitating. These