The main psychoactive constituent of Cannabis was identified as delta-9-tetrahydrocannabinol (THC). In 1986, synthetic delta-9-THC in sesame oil was licensed and approved for the treatment of chemotherapy associated nausea and vomiting under the generic name dronabinol. Clinical trials determined that dronabinol was as effective as or better than other antiemetic agents available at the time. Dronabinol was also studied for its ability to stimulate weight gain in patients with AIDS in the late 1980's. Thus, the indications were expanded to include treatment of anorexia associated with human immunodeficiency virus infection in 1992. Clinical trial results showed no statistically significant weight gain, although patients reported an improvement in appetite.
CB1 and CB2
Within the past 20 years, the neurobiology of cannabinoids has been analyzed. The first cannabinoid receptor, CB1, was identified in the brain in 1988. A second cannabinoid receptor, CB2, was identified in 1993. The highest expression of CB2 receptors is located on B lymphocytes and natural killer cells, suggesting a possible role in immunity. Endogenous cannabinoids (endocannabinoids) have been identified and appear to have a role in, for example, pain modulation, control of movement, feeding behavior, and memory.