Medical Marijuana: Efficacy, Safety, and Potential for Misuse

Lynn R. Webster, MD

Disclosures

March 17, 2010

Question

How does the long-term side effect/adverse event profile and potential for misuse of marijuana compare with those of more common pain medications (ie, opioids)?

Response from Lynn R. Webster, MD
Medical Director, Lifetree Clinical Research and Pain Clinic, Salt Lake City, Utah

Such comparative data would be scientifically useful, but studies have not been performed to date. One risk posed by smoked medical marijuana is that toxins contained in marijuana smoke are reported to contain more tar than tobacco smoke.[1]The risk is not limited to the chemical, delta-9-tetrahydrocannabinol (THC), but extends to other components of the smoke. Marijuana smoke contains more than 60 cannabinoids, each with a slightly different clinical effect.[2] Given the association of illegal marijuana use with problematic opioid use,[3] prescribers who treat chronic pain using opioids may shy away from use of medical marijuana to treat pain.

A possible solution to these problems is the continued development of synthetic THC products. In November 2009, the American Medical Association called for the federal government to consider moving marijuana out of Schedule I to facilitate clinical research and development of cannabinoid-based medications. The American Medical Association also criticized state-based medical-marijuana programs for failing to establish consistent safeguards.

Certain THC products are already in clinical use. Dronabinol (Marinol®), a federal Schedule III drug, is an oral synthetic form of THC that is approved by the US Food and Drug Administration (FDA) for the treatment of AIDS-related anorexia and chemotherapy-induced nausea. In the field of chronic pain treatment, Sativex®, which contains cannabidiol in addition to THC, is approved in Canada as adjunctive treatment for the symptomatic relief of neuropathic pain in multiple sclerosis and for pain due to cancer.[4] Sativex® has received FDA permission to enter into Phase III trials in the United States, and the first large-scale trial for cancer patients is underway.[4] Nabilone is another synthetic analogue of THC that has been used clinically for chronic pain management. Patients taking nabilone for neurogenic pain have been reported to prefer cannabis herb because it relieved not only pain, but also the associated depression and anxiety.[2]

Research into targeting the CB2 cannabinoid receptors in the peripheral nervous system has shown promise in blocking transmission of pain signals while sidestepping the central nervous system involvement associated with cannabis use.[5] Further clinical trials into drugs that target CB2 receptors are planned.

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