TUESDAY, June 23, 2015 (HealthDay News) -- Medical marijuana can be useful in treating chronic pain, but may be less effective for other conditions, a new analysis reveals.
A review of nearly 80 clinical trials involving medical marijuana or marijuana-derived drugs revealed moderately strong evidence to support their use in treating chronic pain, says a report published June 23 in the Journal of the American Medical Association.
The evidence also showed that the medications could help multiple sclerosis patients who suffer from spasticity, which involves sustained muscle contractions or sudden involuntary movements.
But the review found weaker support for the drugs' use in treating sleep disorders; nausea or vomiting related to chemotherapy; for producing weight gain in people with HIV; or for reducing symptoms of Tourette syndrome, a nervous system disorder characterized by repetitive movements or sounds.
The researchers also found no evidence that marijuana-based drugs could help treat psychosis or depression.
"There is evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity," said lead author Penny Whiting, a senior research fellow at the University of Bristol in England.
"However, this needs to be balanced against an increased risk of side effects such as dizziness, dry mouth, nausea, sleepiness and euphoria," she said.
Other common side effects include confusion, loss of balance and hallucination.
The Swiss Federal Office of Public Health commissioned the research team to conduct a systematic review of the effectiveness of medical marijuana products, Whiting said.
The researchers singled out 79 clinical trials for inclusion in their analysis. The studies tested the effects either of medical marijuana itself or drugs that contain plant-derived or synthetic compounds found in marijuana.
For example, they included studies of dronabinol, a U.S. Food and Drug Administration-approved medication that contains synthetic tetrahydrocannabinol (THC), the chemical in pot that produces intoxication.
The authors said that they found and included only two studies that evaluated medical marijuana itself, rather than a derivative medication.
However, Paul Armentano, deputy director of the pro-marijuana group NORML, said many more clinical trials have been conducted involving medical marijuana, but were not included in this analysis.
Armentano also took issue with the report's conclusions regarding treatment of chemotherapy side effects.
"I find the conclusion that there exists only 'low-quality evidence' suggesting that cannabinoids are associated with improvements in nausea and vomiting due to chemotherapy and weight gain in HIV to be a bit perplexing given that the FDA has approved cannabinoids explicitly for these purposes," Armentano said.
"Are we to believe that the FDA approved a pharmaceutical, particularly one as politically charged as a synthetic cannabis pharmaceutical, on the basis of 'low-quality' evidence?" he added.
Dr. Robert Wergin, president of the American Academy of Family Physicians, said that the analysis shows more research is needed on the potential medical benefits of marijuana.
"There are so many compounds in some marijuana products, it's hard to say whether any single one works, either alone or in concert with other compounds," Wergin said. "We need more study and clarification to determine which products are the main contributing factors to the outcomes you're trying to reach."
Wergin added that the federal classification of marijuana as a class I controlled substance is impeding the type of research that needs to be done to clarify the potential benefits.
In an accompanying editorial, two Yale University medical researchers argued for better clinical research before more states adopt medical marijuana laws.
"If the states' initiative to legalize medical marijuana is merely a veiled step toward allowing access to recreational marijuana, then the medical community should be left out of the process, and instead marijuana should be decriminalized," wrote Dr. Deepak Cyril D'Souza and Dr. Mohini Ranganathan of the Yale University School of Medicine in New Haven, Conn.
"Conversely, if the goal is to make marijuana available for medical purposes, then it is unclear why the approval process should be different from that used for other medications," they continued. "Evidence justifying marijuana use for various medical conditions will require the conduct of adequately powered, double-blind, randomized, placebo/active controlled clinical trials to test its short- and long-term efficacy and safety."
Armentano said that the conclusion that marijuana products have some medical benefit "is inconsistent with the plant's federal classification as a schedule I controlled substance possessing no accepted medical utility."
The U.S. government's "reluctance to revisit this 'Flat Earth' position flies in the face of public opinion and available science," Armentano said.
For more on marijuana, visit the U.S. National Institutes of Health.