Four different medical cannabinoids were used in the 17 trials that were evaluated. They contained different levels of cannabidiol (CBD) and tetrahydrocannabinol (THC), the active ingredient in marijuana that makes people high. A lot of uncertainty remains about whether CBD or THC are more effective in relieving MS symptoms – something the JAMA study failed to resolve.

“It is critical that researchers gain a deeper understanding of both of the major (THC and CBD) and minor components of this therapy to unlock its full potential,” said Slaven.

“Given the relative safety of these agents, lack of strong evidence of other effective treatment options, and increasing access in some jurisdictions, it may seem appealing to include cannabinoids in the armamentarium of therapies for MS. But carefully conducted, high-quality studies with thought given to the biologic activity of different cannabis components are still required to inform on the benefits of cannabinoids for patients with MS.

"The bottom line is there is certainly something happening with cannabinoids in regard to symptoms," Nicholas LaRocca, vice president of healthcare delivery and policy research at the National Multiple Sclerosis Society, told HealthDay. "In spite of very strong interest in cannabinoid therapy, we really have relatively little in terms of good research to guide us in terms of what does and what doesn't work, what works for which types of individuals, and so forth."

A small study was recently launched in Australia that might answer some of those questions. Emerald Health Pharmaceuticals of San Diego is using a synthetic version of CBD – called EHP-101 -- to treat about 100 people who suffer from MS or scleroderma, another autoimmune disease. The placebo controlled Phase I trial is meant to determine whether EHP-101 is safe and has any side effects. Results are expected next year.