Smoking marijuana may help relieve the muscle tightness and pain of multiple sclerosis, a small U.S. study suggests.

Many people with MS often suffer from spasticity, an uncomfortable and disabling condition in which the muscles become tight and difficult to control. Spasticity can be controlled with medications but the  symptoms may continue or the anti-spasticity drugs may carry adverse effects such as drowsiness, sedation, and muscle weakness.

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The medical marijuana used in the study the strength of cigarettes most commonly available in the community at the time of the research. (Noah Berger/Associated Press)

Most trials testing medical marijuana have focused on oral forms.

Now a randomized trial has put smoked cannabis to the test against placebo for 30 people with MS whose spasticity resisted treatment.

"Using an objective measure, we saw a beneficial effect of inhaled cannabis on spasticity among patients receiving insufficient relief from traditional treatment," Dr. Jody Corey-Bloom, of the department of neuroscience at University of California, San Diego and her co-authors concluded in Monday's issue of the Canadian Medical Association Journal.

"Smoked cannabis was superior to placebo in symptom and pain reduction in participants with treatment-resistant spasticity."

In the study, the average age of participants was 50 and 63 per cent were female. More than half of the participants needed walking aids and 20 per cent used wheelchairs.

An examiner who did not know which treatment the subjects received assessed the intensity of muscle tone for all participants.

Test lower doses of marijuana

Those smoking marijuana experienced an almost one-third decrease on a scale of spasticity of 2.74 points from a baseline score of 9.3 compared with those smoking a placebo.

Although the marijuana was "generally well-tolerated," smoking it was accompanied by acute cognitive effects such as "feeling too high."

The participants were asked to refrain from smoking marijuana in the month before screening and the three-day testing period. They all had toxicological tests to check.

After 11 days, participants crossed over into the other treatment group so those who'd smoked a placebo then smoked cannabis.

The medical marijuana used in the study contained 4 per cent delta-9-tetrahydrocannabinol, which the researchers said resembled the strength of cigarettes most commonly available in the community at the time of the study.

Two participants withdrew from treatment because they felt uncomfortably "high," two had dizziness and one had fatigue. Another had pain unrelated to the study and another withdrew saying the schedule was too demanding.

The researchers called for more study to see if different doses could help spasticity with less cognitive impact.

The study was funded by the University of California, Center for Medicinal Cannabis Research.