Medical marijuana is on its way to mainstream use but its effects on the nervous system or brain are still a mystery. American Academy of Neurology researchers conducted an analysis of existing studies about the medical cannabis and understand the benefits and disadvantages of marijuana for brain disease treatment.

Researchers reviewed 35 studies and found that there was not enough findings that prove the effectiveness of smoked marijuana. Studies about the medical cannabis are limited and most research were done in Europe because the substance is still highly regulated in the United States. Only 20 states and Columbia have laws that allow doctors to utilize cannabis therapy. Washington and Colorado allow production, consumption and sale of marijuana for non-medical purposes provided it's done the legal way.

While the scientists found that marijuana can help alleviate pain, muscle stiffness and overactive bladder in multiple sclerosis, they found no direct benefit for Parkinson's disease patients and not enough evidence to conclude that it helps epilepsy, Tourette syndrome, cervical dystonia and Huntington's disease patients.

Medical marijuana in oral sprays and pills prove to be effective in MS. "I've known my patients for a long time; they use it, and some will tell me which symptoms they thought it was helpful for," review author Dr. Barbara Koppel from American Academy of Neurology and New York Medical College said. "So we wanted to find out the actual facts - what studies have shown, because that can be a lot different than patient testimonial."

The team also noted that marijuana users reported several dangerous effects such as increased weakness, nausea, suicidal thoughts, mood swings, fatigue and dizziness, intoxicated feelings and hallucinations. There were two reported seizures related to the drug as well.

Marijuana contains around 60 active compounds also known as cannabinoids. The most popular marijuana compound is tetrahydrocannabinol, which gives the "high" effect but can also cause anxiety and psychosis. The cannabidiol is not psychoactive and has opposite effects.

Experts say more research about the effects of marijuana compounds are needed to better understand it as the sample size of the studies was not enough to conclude precise evidence. "We hope the message will come across that there's a huge gap in the literature," University of Kansas Medical Center and review co-author Gary Gronseth said. "A lot more research needs to be done before this is used for most neurological conditions."

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