As medical marijuana makes its way into mainstream clinical use, there is still much mystery surrounding the drug, as not much is known about the its effects on the brain or nervous system disorders.

To gain a better understanding of the benefits – or downsides – of medical cannabis, researchers from the American Academy of Neurology conducted a systematic review of available research analyzing the use of marijuana for the treatment of brain diseases.

Through their analysis, they found that medical marijuana can help alleviate some symptoms of multiple sclerosis (MS), but the drug was not very successful at treating drug-induced movements from Parkinson’s disease. Additionally, there was insufficient evidence to support whether or not marijuana can treat motor problems in Huntington’s disease, tics in Tourette syndrome, or seizures in epilepsy.

According to the researchers, they were interested in reviewing medical marijuana’s effects on brain disorders, as so many patients have started using it as a form of treatment – without a prescription.

“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, of New York Medical College and fellow of the American Academy of Neurology, told FoxNews.com. “So we wanted to find out the actual facts – what studies have shown, because that can be a lot different than patient testimonial.”

For their review, published in the April 29 print issue of the journal Neurology, Koppel and her team analyzed 35 research papers that delved into the effects of medical marijuana use on symptoms of certain neurological disorders. Koppel noted that research on this topic is very limited, and most of the studies utilized came from Europe, since marijuana is still so highly regulated in the United States.

The review found that medical marijuana in pill form and in oral spray form could help treat symptoms of MS – notably spasticity, certain types of pain and overactive bladder. Only a few studies analyzed the benefits of medical marijuana when smoked, but there was not enough to evidence to support its effectiveness.

Koppel said it’s likely that medical marijuana’s effectiveness lies in one of its main ingredients: cannabidiol. When the drug was in the pill form of pure synthetic tetrahydrocannabinol (THC), the active ingredient in marijuana, it wasn’t effective for relieving abnormal movements related to brain disorders. But the pills and spray, which contained a combination of both cannabidiol (CBD) and THC, were found to be the most beneficial for users.

“The THC, that’s what makes you high when you smoke marijuana,” Koppel said. “…We have different receptors in our brain for [THC and cannabidiol], and the THC works on the ones in the limbic system; they effect memory, give you hallucinations, but on the other hand, they can make you feel happy. The other receptors are in the brain that control abnormal movement, spasticity, and motor control. So [the results are] depending on what part of the brain you’re trying to activate.”

The AAN review concluded there is no definitive proof to suggest that medical marijuana is effective for Parkinson’s disease, Huntington’s disease, Tourette syndrome, cervical dystonia (abnormal neck movements), or seizures from epilepsy. Additionally, the researchers noted that users of marijuana reported a number of dangerous side effects – including nausea, increased weakness, mood changes, suicidal thoughts, hallucinations, dizziness and fatigue, and feelings of intoxication. Two seizures were also reported in relation to the drug.

These warnings also coincide with a study recently published in the Journal of Neuroscience, which found that casual marijuana use – using cannabis just once or twice a week – may cause significant abnormalities in certain key brain structures. Koppel said her study strictly looked at medical marijuana, which is created to be far less damaging than recreational pot.

“It’s nothing like what they’re selling on the streets,” Koppel said. “We’ve known about that end of the spectrum for a long time. It’s not safe cognitively, and it can have some permanent harm. But it’s one of the reasons I’m glad we can put the whole discussion on the table.”

With so few studies to choose from, Koppel hopes her review will inspire more researchers to study the effects of medical marijuana on the brain. Although they didn’t find much evidence to suggest cannabis can treat these neurological disorders, Koppel noted the drug still has the potential to help.

“There’s a place for it, especially for people whose spasticity is not controlled by anything else,” Koppel said. “If their main symptom of MS is spasticity, this might benefit them.”