Strong evidence still lacking on medical marijuana for pain

Mark Ware, M.D., executive director, Canadian Consortium for the Investigation of Cannabinoids and director of clinical research, Alan Edwards Pain Management Unit, McGill University Health Center, moved to Canada in 1999 following a court decision that legalized marijuana there. He had been working in Jamaica at a sickle-cell anemia clinic, where he encountered several patients who told him that using marijuana eased their pain. At McGill University, Ware evaluates claims from patients about the medical benefits of marijuana and is involved in research on the long-term safety of the plant in patients using it for chronic conditions.

"Much of what we know about medical marijuana is anecdotal, so the challenge is to recognize that patients who say they get pain relief by self medicating with marijuana may be right, and move forward in conducting more scientific studies to better understand its analgesic benefits and overall safety," said Ware.

The New York Times has reported that worldwide some 15 trials of medical cannabinoids have been conducted. Results have shown effectiveness in reducing pain from neuropathy, diabetes and fibromyalgia.

The FDA has approved two cannabinoid medications, dronabinal and nabilone. They are prescribed for controlling nausea and vomiting caused by chemotherapy and to treat anorexia in HIV patients. Other cannabinoid-based medications are under FDA review for treating cancer pain and other conditions.

Ware said several challenges lie ahead for conducting marijuana pain studies. "With legalization of medical marijuana in more than 20 states, widespread access will yield more reports that need to be evaluated," said Ware. "And, while it's clear that large, Phase 3 clinical trials are needed to better understand medical marijuana's potential clinical efficacy, who will pay for them and is it necessary to conduct trials for every pain condition that could be treated with marijuana?"

Another obstacle for medical marijuana research, according to Ware, is lack of standardized products. "Plants grown in Colorado and other legalization states could be different, so when talking about cannabis in various states, there could be a variety of compounds," he said. According to the National Institute on Drug Abuse, most marijuana used as medicine is the same quality and carries the same health risks as marijuana sold on the street.

New studies also are needed to explore safety problems. "There are safety concerns about the molecule itself, and studies of recreational marijuana users show the drug can affect the brain and lungs. Questions also arise about smoking as a safe route of administration vs. oral dosing," Ware stated.

In states where medical marijuana is legal, physicians have discretion in advising patients about using it for pain management. "Doctors are being asked every day if using marijuana can lessen pain intensity," said Ware. "Even though there are no efficacy and safety data from large controlled clinical trials, doctors interested in medical marijuana should learn about the plant itself and its myriad active ingredients by reviewing the scientific literature, understanding local legal issues and potential liability, and weighing the risks and benefits vs. other analgesics, including opioids."