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Cannabis has been used recreationally and medically for centuries. Despite long experience, relatively little is known about the risks and benefits of its use as a medication. A considerable portion of our ignorance can be attributed to government discouragement of cannabis research. Searching the NIH website brings up many studies of both cannabis abuse and cannabis as a therapeutic agent, but most of the general information available is about cannabis as a drug of abuse.

And there is no doubt about the abuse potential and withdrawal potential of marijuana except among hard core denialists. The data is clear: marijuana discontinuation is associated with a withdrawal syndrome in many users, with some experts likening it in symptoms and severity to nicotine withdrawal.

As with any pharmacologically active substance, there are no “side effects”, only effects which we desire and those we do not. Given that cannabis is clearly a powerful pharmacologic agent, that there is a great deal of anecdotal evidence supporting its use, and that there is scientific plausibility to these claims, its potential use as a therapeutic drug should be investigated seriously.

As marijuana becomes increasingly available for medical use, practitioners of science-based medicine need to evaluate the evidence for the use of this drug. In evaluating a new drug, we must ask a number of questions, including those of safety, efficacy, and perhaps redundancy. Claims for the efficacy of marijuana tend to be hyperbolic, with no condition being exempt from its benefits. The state of Michigan passed a law last year allowing the use of medical marijuana. The statue requires a doctor to attest to the following:

It is my professional opinion that the applicant has been diagnosed with a debilitating medical condition as indicated above. The medical use of marihuana is likely to be palliative or provide therapeutic benefits for the symptoms or effects of applicant’s condition.

Once a patient has this certification, they are allowed to grow a small amount of pot for their own use.

What conditions does this apply to?

Cancer

Glaucoma

HIV or AIDS Positive (sic)

Hepatitis C

Amyotrophic Lateral Sclerosis

Crohn’s Disease

Agitation of Alzheimer’s Disease

Nail Patella OR a medical condition or treatment that produces, for this patient, one or more of the following and which, in the physician’s professional opinion, may be alleviated by the medical use of medical marihuana. Cachexia or Wasting Syndrome

Severe Chronic Pain

Severe Nausea

Seizures (Including but not limited to those characteristic of Epilepsy)

Severe and Persistent Muscle Spasms (Including but not limited to those characteristic of Multiple Sclerosis.)

“Cancer” means so many different things as to be nearly meaningless. What if in my professional opinion the patient’s basal cell cancer might be improved with a toke? Leaving this aside, what evidence do we have that marijuana is safe and effective in the listed conditions, and that it has a better risk/benefit profile than extant treatments?

For example, a recent review of marijuana for for the use of muscle spasticity in multiple sclerosis found little objective evidence for its benefit. Glaucoma, one of the original “indications” for medical marijuana, is a condition for which many sophisticated and effective interventions exist, but the literature for the use of cannabis for this disorder is anemic to say the least.

The use for marijuana for many of these indications barely passes the plausibility test. Of what possible use could pot be in the treatment of hepatitis C or Crohn’s disease? The agitation of Alzheimer’s could just as plausibly be exacerbated by pot as palliated, and a recent review found no benefit.

Some areas with better plausibility include cachexia (weight loss due to chronic disease) and nausea, although the development of drugs such as ondansetron, with its minimal side-effects and excellent anti-emetic activity makes pot look redundant at best.

Dronabinol, a synthetic and legal marijuana-based drug has been used for a number of years for nausea and appetite loss, but the data have not been all that encouraging.

Marijuana offers many promising avenues of investigation, although there will be little advancement without a change in US government policy. But for a physician, the reason for the lack of data is not nearly as important as the lack of data itself. As physicians, we cannot ethically prescribe or recommend a powerful pharmaceutical whose effects are not at least reasonably well-known. In fact, it’s hard to envision any situation in which prescribing marijuana would be ethical. If there were a condition with a lot of anecdotal data and no other effective treatment, and the risks of the condition were such that they outweighed the health risks and dependence potential of marijuana, we would maybe—maybe—have something to work with. But for now, people who want to take cannabis should not count on a doctor to approve it for them.