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IOM Finds Scientific Merit to Medical Marijuana

April 1999

The Institute of Medicine has finally completed its review of evidence concerning marijuana potential benefits and risks for medical use. The Institute, or IOM, is a branch of the National Academy of Sciences. Its report comes in the aftermath of voter referenda that supported the legalization of marijuana as medicine in California and Arizona and five other states. The IOM panel's conclusions mark another step forward in marijuana's acceptance for such uses as suppression of nausea, relief from pain and stimulation of appetite in people with HIV or AIDS. (The 250-page report, "Marijuana and Medicine: Assessing the Science Base," can be ordered over the Internet at, the National Academy Press web site. An executive summary and prepublication text are also available at that web site.)

The special IOM marijuana advisory panel purportedly sought to stick to the "solid ground of scientific consensus," which required de-emphasizing "belief-based medicine" and social and legal arguments. Investigators analyzed reports in the mainstream scientific literature, visited buyers' clubs, and solicited the input of scientists well versed in the most up-to-date research on cannabinoids.

The report defines marijuana as "unpurified plant substances, including leaves or flower tops, whether consumed by eating or smoking," and the effects of marijuana as "the composite effects of its various components" including marijuana's main active ingredient, THC, and other related cannabinoids. The panel sought to better understand three things: the effects of cannabinoids, the health risks related to medical marijuana, and the efficacy of medical marijuana.

Science Notes

Scientific advances in the past 16 years that include the identification of cannabinoid receptors in the brain have allowed for a much better understanding of both the effects of THC and other cannabinoids, and the potential for medical benefits. Over the past 16 years, various cannabinoid-based drugs, such as Marinol, also have been developed. Cannabinoid drugs are indicated for relief of pain and nausea and for appetite stimulation. These drugs have been identified to be particularly relevant for people who suffer simultaneously from pain and appetite suppression, such as people with HIV/AIDS and people undergoing chemotherapy.

Cannabinoids offer broad-spectrum relief to those with HIV/AIDS, yet marijuana is not without its adverse effects. One problem with marijuana is common to all medicinal plants: The biologically active ingredients occur in varying amounts, and this makes the effect impossible to predict exactly. A greater problem concerns the toxins contained in marijuana smoke, which are the same as those found in tobacco smoke.

The Outcome: Conclusions and Recommendations

The IOM panel says it found "substantial consensus among the experts in the relevant disciplines on the scientific evidence." Cannabinoids play a natural role in pain modulation, which is multifaceted but remains unclear insofar as it relates to the immune system. While tolerance develops and the potential for dependence exists, data from animal research suggest that a narrow set of conditions provide for the possibility of tolerance, making it less likely than with other substances approved for use such as benzodiazepines (such as diazepam or Valium) or nicotine. Because different cannabinoid receptors appear to play different roles, while some appear uninvolved in mediating some effects of cannabinoids, research should continue to evaluate the effects of THC alone and in combination with other cannabinoids.

THC and cannabidiol, the precursor of THC, are the two most abundant cannabinoids in marijuana as well as the two most studied. Overall, it appears that their effects on symptoms such as pain and nausea are modest. For many people, other drugs are more effective, but, as the report notes, many people do not respond well to the other available medications. In addition, cannabinoids offer broad-spectrum relief; they are particularly well suited to people with relevant complaints (i.e., nausea, vomiting, anorexia, headache and pain) -- again, people with AIDS, particularly those with wasting, and people undergoing chemotherapy.

Cannabinoids also have psychological effects including anxiety reduction that need further evaluation in clinical trials. While these effects are often helpful -- for instance, reducing anxiety appears itself to lessen the pain -- mood alteration is upsetting for some patients, especially older ones.

Health Risks

There are two main conclusions about the health risks. One, excluding risks related to smoking, the adverse effects of marijuana are within a range accepted for other medications. There are short- and long-term effects of marijuana. Acute marijuana diminishes psychomotor performance -- therefore, for example, driving a car is not advisable while under the influence. Two, there may be short-term immunosuppressive effects that require further study, although the report suggests that these are not likely to be serious enough to rule out prescribed usage.

For a few persons, chronic THC use may involve psychological dependence. Risk factors include antisocial personality and conduct disorders, which are risk factors for other forms of substance abuse as well. Further, no evidence suggests that use of medical marijuana, particularly if regulated as are other medications with "abuse potential," would cause an increase in its use among the general population. The report notes that questions about causality and drug abuse are somewhat beyond the appropriate scope of a discussion of the medical uses of marijuana.

Finally, most studies that have claimed to detect a harmful effect of marijuana have been based on smoked marijuana, so that the effects of cannabinoids were not distinguished from the effects of burning plant materials and toxins. Smoking is associated with abnormal changes in respiratory cells and tissue and with increased risk of cancer, lung disease, and poor pregnancy outcome. These emerge as arguably the most pressing risks, somewhat anticlimactically (given the historic florid, anti-marijuana hype).

Back to the GMHC Treatment Issues April 1999 contents page.

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See Also
More Research on Medical Marijuana