"We wanted to inform patients and physicians, but we didn't make specific treatment recommendations," said study coauthor Dr. Gary Gronseth, a professor of neurology at the University of Kansas Medical Center in Kansas City.

But the review, conducted by specialists convened by the American Academy of Neurology, found that marijuana does not help relieve the uncontrollable limb spasms that result from a drug used to treat Parkinson's disease. And it concluded that there is insufficient evidence to know whether the drug reduces symptoms caused by neurological diseases such as Huntington's disease, Tourette's syndrome, or epilepsy.

With medical marijuana dispensaries set to open later this year in Massachusetts, a review of the latest research suggests that it can help alleviate multiple sclerosis symptoms such as pain, overactive bladder, and muscle stiffness.


He and his colleagues recommended that doctors consider potentially serious side effects before certifying patients to grow or buy the drug. Mood changes, depression, hallucinations, or suicidal thoughts occurred in about 1 percent of patients who used marijuana for medical purposes, according to the review of 34 studies published Monday in the journal Neurology, Other side effects included nausea, increased weakness, dizziness, fatigue, and feelings of intoxication.

"While certain forms of medical marijuana can be helpful to treat some symptoms of MS, our review highlights the need for more high quality research studies on the safety and efficacy of marijuana," said Dr. Barbara Koppel, the study leader and a neurologist at New York Medical College in New York.

Despite those concerns, the conclusions of the neurology group's review could make neurologists more likely to recommend marijuana — taken as a pill, squirted into the mouth in spray form, or smoked — to MS patients who fail to benefit from standard treatments.

"I think it is a positive finding, and it makes me feel more comfortable telling patients to use medical marijuana," said Dr. Howard Weiner, director of the Partners MS Center at Brigham and Women's Hospital.


Since January, he and his colleagues have certified more than 100 of their multiple sclerosis patients to use marijuana for medical purposes.

Until dispensaries open, certified patients can grow their own marijuana or obtain it from a "personal caregiver" such as a hospice provider or visiting nurse.

Most of the studies included in the review assessed medical marijuana in pill or spray form, rather than smoked; it is harder for researchers to determine the level of active compounds patients get with each inhale, so they prefer to use more standardized forms of delivery.

Koppel said in a press briefing that the latest evidence suggests that certain chemicals in the plant called cannabinoids provide more relief from multiple sclerosis symptoms with fewer side effects than tetrahydrocannabinol, or THC, the compound that produces the feeling of being high. More research, however, is needed to determine which formulation works best.

The National Multiple Sclerosis Society said in a statement that it "supports the rights of people with MS to work with their health care providers to access marijuana for medical purposes" but added that "current research is unable to fully determine whether smoked marijuana is safe or helpful for treating MS symptoms."

While the study authors found that THC pills were not effective combating involuntary muscle movements caused by the Parkinson's drug levodopa, they could not conclude one way or the other whether medical marijuana in any form could help alleviate a wide variety of symptoms caused by other neurological diseases such as epileptic seizures, Tourette's syndrome tics, abnormal neck movements, or paralysis caused by Huntington's disease.


"Saying there's insufficient evidence is not the same thing as saying that [medical marijuana] is not effective for these conditions," Gronseth said.

In January, the state Department of Public Health approved 20 applicants for preliminary licenses to operate dispensaries, but last month those applicants were told they would have to undergo extensive additional background checks. It is unclear whether the new round of scrutiny will delay the opening of the dispensaries.

Matthew Allen, executive director of the Massachusetts Patient Advocacy Alliance, said there is an "urgent need" for the dispensaries to be open as soon as possible.

Any lack of effectiveness seen in the review, he added, is the result of federal policies that have made it extremely difficult for researchers to obtain the controlled substance.

"These policies must be changed to allow more study of medical marijuana," he said in an interview.

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.