Medical Marijuana: Where’s the Evidence?

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With many US states now having laws in place to facilitate access to medical marijuana for a variety of medical conditions, two new reviews have highlighted the lack of evidence to support its use in most indications.

An editorial also raises questions about the legal implications for doctors prescribing such products.

The reviews, published in the June 23/30 issue of JAMA, note that 23 states and the District of Columbia have enacted laws to allow prescription of medical marijuana for certain medical conditions.

Reviewing the medical literature on medical marijuana, the two papers come to similar conclusions — that some evidence supports the use of marijuana for nausea and vomiting related to chemotherapy, specific pain syndromes, and spasticity from multiple sclerosis. But for most other indications such as hepatitis C, Crohn’s disease, Parkinson’s disease, or Tourette’s syndrome, they found that the evidence supporting its use is of poor quality.

A third paper in the same issue of JAMA highlights the large variability in specific cannabinoids in various medical marijuana products and finds that contents did not conform to what was advertised on the labelling.

In an accompanying editorial, Deepak Cyril D’Souza, MBBS, and Mohini Ranganathan, MD, Yale University School of Medicine, New Haven, Connecticut, note that for most of the conditions that qualify for medical marijuana use, the evidence fails to meet US Food and Drug Administration (FDA) standards.

They call for government support to conduct high-quality trials. Until such trials are available, they suggest it may be prudent to wait before widely adopting use of marijuana. “Perhaps it is time to place the horse back in front of the cart,” they conclude.

Legal implications Unclear

The editorialists point out that for physicians, the legal implications of certifying patients for medical marijuana remain unclear given the differences between the views of state vs federal government.

They emphasize that the prescription, supply, or sale of marijuana is illegal by federal law, and it is not known to what extent a physician who certifies a patient for medical marijuana may be liable for negative outcomes, and whether malpractice insurance will cover any liability.

In one of the review papers, Kevin P. Hill, MD, McLean Hospital, Belmont, Massachusetts, examined 28 randomized clinical trials of cannabinoids in various indications.

He notes that there are two cannabinoids (dronabinol and nabilone), which are FDA approved for nausea and appetite stimulation.

Apart from these two indications, Dr. Hill found that use of marijuana for chronic pain, neuropathic pain, and spasticity due to multiple sclerosis is supported by high-quality evidence.

Six trials that included 325 patients examined chronic pain, 6 trials that included 396 patients investigated neuropathic pain, and 12 trials that included 1600 patients focused on multiple sclerosis. Several of these trials had positive results, suggesting that marijuana or cannabinoids may be efficacious for these indications.



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