Medical marijuana may help relieve some multiple sclerosis symptoms but has several safety concerns

Certain forms of medical marijuana can help treat some symptoms of multiple sclerosis (MS), but they do not appear to be helpful in treating drug-induced movements in Parkinson's disease, a review by the American Academy of Neurology found.

The review was published in the April 29 Neurology and was presented at the academy's annual meeting in Philadelphia. Thirty-four studies met inclusion criteria; 8 were rated as Class I.

The review concluded that medical marijuana only in pill or oral spray form can help treat some symptoms of MS, including spasticity; certain types of pain related to spasticity, including painful spasms and painful burning and numbness; and overactive bladder. Most of the studies examined pill or oral spray forms of medical marijuana. There were 2 studies that examined smoked medical marijuana for treating MS symptoms. However, the studies did not provide enough information to show if smoked medical marijuana is effective.

For Parkinson's disease, the review concluded that use of synthetic THC pills likely does not help relieve abnormal movements that can develop in the late stages of the disease from the drug levodopa.

The review also noted safety concerns with medical marijuana, including nausea, increased weakness, behavioral or mood changes, suicidal thoughts or hallucinations, dizziness or fainting symptoms, fatigue, and feelings of intoxication. There was one report of a seizure.

The researchers excluded studies that reanalyzed earlier studies, used a single dose of medication, or had Class IV evidence or unclear information about them. Overall, 1,619 patients were treated with cannabinoids for less than 6 months. Meta-analysis of simple proportions revealed that 6.9% (95% CI, 5.7% to 8.2%) stopped the medication because of adverse events, compared to 2.2% who received placebo (95% CI, 1.6% to 3.5%).

A study of patients with MS who smoked cannabis at least once a month showed an increase in cognitive impairment. Another article showed that patients with MS who used cannabis were twice as likely to be classified as globally cognitively impaired as those who did not use cannabis. Some patients who have neurologic conditions may have preexisting cognitive dysfunction, which may increase their susceptibility to cannabinoids' toxicities. Moreover, it is especially concerning that a medication that may have an associated risk of suicide may be prescribed in a population that is already at increased suicide risk, the reviewers noted. The studies showed that the risk of serious psychological effects is about 1%.

The review also concluded there was not enough evidence to support using medical marijuana for motor problems in Huntington's disease, tics in Tourette's syndrome, cervical dystonia, or seizures in epilepsy.