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But does it truly help with medical ailments?Wikimedia Commons/Torben Hanse

The medical benefit of cannabis isn't all that it's cracked up to be, according to the largest review study to date on potential marijuana health effects.

Marijuana does seem to provide moderate relief for people in pain, including patients suffering from chronic nerve pain or cancer pain, as well as help people who have multiple sclerosis and experience muscle spasms, according to a new examination of hundreds of studies of medical marijuana.

But it appears to have very little impact on several other conditions for which it's used, including sleep disorders, Tourette syndrome, anxiety disorders, depression or psychosis, HIV-related weight loss and nausea, said the study in the Journal of the American Medical Association.

But the scientists also said many studies were small or their scientific process flawed, and called for more and more rigorous research into the medical effects of cannabinoids, the compounds that are the active ingredients in cannabis.

"There is evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity," said study co-author Penny Whiting, a research fellow in epidemiology and health services research at the University of Bristol in the UK. "However, this needs to be balanced against an increased risk of side effects," which can include dizziness, dry mouth, nausea and sleepiness, she added. "Individuals considering cannabinoids as a possible treatment for their symptoms should discuss the potential benefits and harms with their doctor."

The study was commissioned by the Swiss Federal Office of Public Health.

Twenty-three states in the US have approved medical marijuana with the idea that cannabis treats a variety of ailments.

Support to use the drug for certain health problems has "relied on low-quality scientific evidence, anecdotal reports, individual testimonials, legislative initiatives and public opinion," wrote Dr. Deepak Cyril D'Souza and Dr. Mohini Ranganathanof the Yale University School of Medicine in an editorial accompanying the new study. "Imagine if other drugs were approved through a similar approach."

The new review, analysed information from nearly 80 studies that included about 6,500 people total, in which participants were randomly assigned to take cannabinoids, a placebo or another drug.

In more bad news for stoners, a separate study in the same journal found that THC content was far less than advertised in 62 of 75 edible marijuana products tested.