MONDAY, April 28, 2014 (HealthDay News) -- Medical marijuana can help relieve some symptoms of multiple sclerosis, but whether it can benefit patients with other neurological disorders is still unclear, according to a new review by top neurologists.
Doctors with the American Academy of Neurology reviewed current research and found certain forms of marijuana -- but not smoked marijuana -- can help treat MS symptoms such as muscle stiffness, certain types of pain and muscle spasms, and overactive bladder.
"There are receptors in the brain that respond to marijuana, and the locations of the receptors are in places where you would expect them to help with these symptoms," said Dr. Barbara Koppel, a professor of neurology at New York Medical College in New York City and a fellow of the American Academy of Neurology.
But marijuana can't help tremors caused by MS or involuntary muscle spasms caused by the use of levodopa to treat Parkinson's disease, the physicians concluded.
Their review included other neurological disorders such as Huntington's disease, Tourette syndrome and epilepsy, but the doctors found too little quality research to determine whether medical marijuana can help these conditions.
"We were frustrated that we couldn't say that it's good for this or bad for that. It's just a function of the lack of studies that were usable," Koppel said. "We see this review as a starting point for having more studies get done so we can review them down the road."
The academy's guideline development subcommittee presented the review Monday at the academy's annual meeting in Philadelphia, the world's largest gathering of neurologists. It also is published in the April 29 issue of Neurology.
The panel of experts looked at more than 1,700 study abstracts before focusing on 34 studies that dealt specifically with brain disorders.
Their findings recommend the use of medical marijuana for MS only if taken in pill or spray form, not by smoking it, Koppel said.
Converting marijuana to pill or spray form allows doctors to control the dose that patients receive of the drug's two medically helpful ingredients -- tetrahydrocannabinol, or THC, which gets a person high, and the nonpsychoactive component cannabidiol, or CBD.
If patients smoke their medical pot, there's no way to tell how much of either ingredient they receive, she said.
"There's a lot of work going on to find another delivery system so you can be sure what you're getting, how much is THC and how much is CBD," Koppel said.
The review included two 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.
The literature review also warned doctors to be mindful of the potential for harmful side effects, including thinking and memory problems, from medical marijuana. Mood changes and suicidal thoughts are of special concern for people with MS, who are at an increased risk for depression or suicide. The studies showed the risk of serious psychological effects is about 1 percent, or one in every 100 people.
NORML, the organization for the reform of marijuana laws, said the research came up short. Deputy director Paul Armentano disputes the authors' claims that there wasn't enough evidence to make broader conclusions about medical marijuana's benefits.
A review of the available literature "reveals some 20,000 published papers on cannabis and cannabinoids, including well over 100 controlled trials evaluating their safety and efficacy," Armentano said. "It is inaccurate to allege that information pertaining to cannabis' safety or therapeutic utility is lacking."
Advocates for people with MS, a disease of the nervous system, welcomed the review. The National MS Society "supports the rights of people with MS to work with their health care providers to access marijuana for medical purposes in accordance with legal regulations in those states where such use has been approved," said Timothy Coetzee, the society's chief advocacy, services and research officer.
The society also supports the need for more research to better understand the benefits and potential risks of marijuana and its derivatives as a treatment for MS, Coetzee said. "We intend to work towards removing barriers impeding such research," he added.
There is no cure for MS, but medications slow it down and help control symptoms for some people. Medical marijuana is usually not recommended unless standard treatments fail.
For more information on marijuana, visit the U.S. National Institutes of Health.