After an 11-day "washout" period, the men and women returned for another session. Again, they smoked either the marijuana or a placebo once daily for three days. This time, they were assigned to the opposite group.
Before and after each session, the researchers measured the participants' muscle stiffness using an accepted scale. They also evaluated pain levels, tested certain thinking skills and looked at fatigue levels.
On average, the patients had about a three-point reduction on the spasticity scale. "It's a modest effect," said Corey-Bloom.
"It also reduced the patients' perception of pain," she added. Pain scores showed a 50 percent decrease in perceived pain.
Downsides included increased fatigue, she said. Cognitive (thinking) skills also declined in the pot-smoking participants. "There were some short-term, modest effects on cognition -- primarily attention and concentration," she noted.
The pot probably works, she said, by acting on special receptors in the brain involved in controlling muscle spasticity.
Nicholas LaRocca, vice president of health care delivery and policy research at the National Multiple Sclerosis Society, said the study was well done.
"For people with MS, spasticity is a major problem," he said. "Although treatments are available, they don't work for everyone with MS."
While the study showed good short-term effects of the cannabis, LaRocca said, "the study does show that smoking marijuana is not a long-term solution, because of the cognitive effects."
People with multiple sclerosis are already likely to have cognitive defects, he noted.
"We need to continue to search for not only other medicines for plasticity, but nonpharmacologic treatments," LaRocca said.
The study was funded by the University of
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