A National Institutes of Health (NIH) panel of experts has concluded that critical questions about the therapeutic usefulness of marijuana remain largely unanswered by studies that have been conducted to date. The panel called for NIH to facilitate rigorous, well-designed clinical studies to evaluate marijuana's potential to treat a variety of medical conditions. Such studies must address the many potential short- and long-term hazards of smoked marijuana, the panel stressed.
The panel of eight experts, who have broad experience in clinical studies and therapeutics, expressed their opinions in a 37-page report that NIH issued in August 1997. NIH had convened the experts at a 2-day meeting earlier in the year to consider wide-ranging claims about the therapeutic usefulness of marijuana, particularly smoked marijuana, and the need for and feasibility of additional research. At the meeting, the panel reviewed the published scientific data on the medical use of marijuana and considered comments, including those from patients and advocacy groups.
Under U.S. law, marijuana has been classified in the most restrictive category of controlled substances since 1970. This means that the drug in its usual form has a high potential for abuse and has no commonly accepted medical use in this country. However, advocates for the medical use of smoked marijuana claim it is effective in such areas as reducing nausea associated with cancer chemotherapy, counteracting the wasting syndrome associated with AIDS, and treating glaucoma. An oral form of marijuana's principal active ingredient, delta-9-tetrahydrocannabinol (THC), called dronabinol, is approved as a treatment for nausea and vomiting related to cancer chemotherapy. Dronabinol also is used to stimulate the appetite of AIDS patients.
The NIH panel noted that the current debate over using marijuana as a medicine centers on claims that smoked marijuana offers therapeutic advantages over dronabinol and that it has potential to treat other conditions, such as pain and glaucoma. However, little data from clinical trials are available to support or refute these claims, the panel's review showed.
Most previous studies of marijuana's therapeutic potential have used THC in capsule form. Such studies do not answer questions about the potential benefits or risks of smoked marijuana, which has substantially different dose absorption and pharmacological activity from the oral dosage form, the panel noted. In addition, although THC is the principal psychoactive component of the cannabis leaf, other compounds in the leaf may have therapeutic properties, the panel said.
The panel called for more studies to properly evaluate marijuana's medical potential in five areas: analgesia, or pain relief; neurological and movement disorders; nausea and vomiting associated with cancer chemotherapy; glaucoma; and appetite stimulation to counteract weight loss in patients with AIDS or cancer. In addition to dronabinol, effective treatments already are available for many of these indications, the panel noted. For example, a number of medications can treat pain without risking marijuana's adverse effects.
However, even where effective medications exist, marijuana could be studied for its potential to offer relief to patients who do not respond fully to such treatments, the panel stated. Other reasons for studying marijuana's medical potential include determining whether it is useful in treating diseases or conditions for which treatments are not currently available, such as nerve pain caused by disease or tissue injury, and whether it could enhance the therapeutic effects of currently available treatments.
Any studies of marijuana's medical potential need to consider both the short- and long-term risks associated with smoked marijuana, the panel stressed. Among the short-term risks cited by the panel are cardiovascular effects, effects on the lungs, and undesirable mental and behavioral effects. Other concerns would come into play if marijuana were used to treat patients with chronic diseases, such as the possibility that frequent and prolonged marijuana use might significantly impair the functioning of the 's immune system. Examining that aspect is particularly important for patients who already have compromised immune systems, such as cancer patients undergoing chemotherapy and HIV/AIDS patients, the panel noted.
To address health concerns about using smoked marijuana for longer term therapy, the panel suggested that researchers strive to develop alternative dosage forms for marijuana, such as a smoke-free inhaled delivery system. Such a system could deliver purer forms of THC and related cannabinoids and permit better control of doses, the panel stated.