Evidence of Marijuana’s Medical Usefulness Mounts

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New research conducted by Penny Whiting, a senior research fellow at the University of Bristol, supports use of marijuana for chronic pain and neuropathic pain, as well as spasticity due to multiple sclerosis. Alessandro Bianchi/Reuters

The current issue of The Journal of the American Medical Association (JAMA) includes two articles that review studies of marijuana's medical utility and come to similar conclusions about the applications that are best supported by the existing evidence: treatment of chronic pain, neuropathic pain and spasticity.

There is also substantial evidence that THC, marijuana's main active ingredient, is effective at relieving nausea and restoring appetite.

In a review commissioned by the Swiss Federal Office of Public Health, Penny Whiting, a senior research fellow at the University of Bristol, and her co-authors consider 79 randomized clinical trials of cannabinoids involving about 6,500 subjects. Only two of the studies assessed marijuana itself; the others involved marijuana-based medications such as Marinol (synthetic THC in capsules) and Sativex (an oral spray containing cannabis extract).

Per the Swiss government's instructions, Whiting et al. looked for evidence of cannabinoids' effectiveness in treating nausea and vomiting due to chemotherapy, loss of appetite associated with HIV/AIDS, chronic pain, spasticity due to multiple sclerosis or paraplegia, depression, anxiety disorder, sleep disorder, psychosis, glaucoma and Tourette's syndrome.

"There was moderate-quality evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity," the researchers conclude. "There was low-quality evidence suggesting that cannabinoids were associated with improvements in nausea and vomiting due to chemotherapy, weight gain in HIV, sleep disorders and Tourette syndrome."

Where evidence was deemed inadequate, the main issues were a lack of statistical significance and possible sample bias due to subjects who dropped out of the studies before they were completed.

The researchers' conclusions regarding nausea, vomiting and appetite loss are rather surprising, since the Food and Drug Administration (FDA) deemed the evidence strong enough to approve synthetic THC as a treatment for these symptoms.

In fact, the author of the other medical marijuana review in this issue of JAMA, Kevin Hill, a psychiatrist who runs the Substance Abuse Consultation Service at McLean Hospital, does not include studies of these applications, apparently viewing them as well established in light of FDA approval.

Based on 28 randomized clinical trials of cannabinoids and applying somewhat different criteria than Whiting et al., Hill concludes that "use of marijuana for chronic pain, neuropathic pain, and spasticity due to multiple sclerosis is supported by high-quality evidence."

Hill seems to agree with Whiting et al. that the evidence supporting marijuana as a treatment for glaucoma, anxiety, depression, sleep disorders and Tourette's syndrome is markedly weaker. In addition to those, qualifying conditions listed by various state medical marijuana laws include epilepsy, hepatitis C, lupus, fibromyalgia, Crohn's disease, Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and post-traumatic stress disorder.

Some laws allow the use of marijuana to treat additional conditions beyond those listed, either based on a determination by state health officials or at the discretion of doctors who write recommendations.

In an editorial accompanying the JAMA review articles, Yale psychiatrists Deepak Cyril D'Souza and Mohini Ranganathan express dismay at the proliferation of conditions that cannabis supposedly can be used to treat.

"There is some evidence to support the use of marijuana for nausea and vomiting related to chemotherapy, specific pain syndromes and spasticity from multiple sclerosis," they say. "However, for most other indications that qualify by state law for use of medical marijuana, such as hepatitis C, Crohn disease, Parkinson disease, or Tourette syndrome, the evidence supporting its use is of poor quality."

They argue that the conditions recognized by state laws are determined by politics rather than science and that marijuana-based medicines should be subject to the same FDA approval process as any other pharmaceutical, which requires double-blind, randomized clinical trials.

"If the states' initiative to legalize medical marijuana is merely a veiled step toward allowing access to recreational marijuana," D'Souza and Ranganathan say, "then the medical community should be left out of the process, and instead marijuana should be decriminalized. 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."

There are various possible rejoinders to this argument, based on marijuana's remarkable safety compared with most pharmaceuticals, the long history of its use as a medicine and the federal government's obstruction of research aimed at verifying the plant's therapeutic potential (which the Obama administration is only now beginning to address).

But D'Souza and Ranganathan have a point: Medical marijuana advocates are asking for special treatment of cannabis, something that offends the technocratic sensibilities of organized medicine. Then again, all they are seeking is the right to treat themselves with a plant they find useful, regardless of whether rigorous research has confirmed what they believe they have learned from their own experience.

That is a basic human right, although exercising it may entail a lot of trial and error, not to mention unscientific conclusions. There is nothing wrong with pointing out the latter, as long you don't insist on using force to prevent people from acting on them.

Jacob Sullum is a senior editor at Reason magazine