The present paper describes the historical use of cannabis, starting with its use in Assyria and China. Recent advances in the understanding of the molecular basis of cannabis action are explained, including the identification of the cannabinoid receptors CB(1) and CB(2), as well as the isolation of endogenous cannabinoids from the brain and periphery. The use of delta(9)-tetrahydrocannabinol as an anti-vomiting and anti-nausea drug for cancer chemotherapy, and as an appetite-enhancing agent is described. Clinical work in multiple sclerosis, which may lead to the approval of tetrahydrocannabinol as a drug for this condition, is presented. Preclinical and clinical investigations with cannabidiol, a non-psychotropic cannabis constituent, are also described. Recent work with cannabidiol in animal models of rheumatoid arthritis may lead to clinical investigations. A synthetic cannabinoid, HU-211 (Dexanabinol), is in advanced clinical stages of investigation as a neuroprotectant in head trauma. The above clinical approaches may ultimately lead to the realization that cannabinoids are valuable clinical drugs in numerous fields.