This is an exciting time for cannabinoid research. Evidence suggests that cannabis (marijuana) can alleviate symptoms like muscle spasticity and pain in patients with multiple sclerosis (MS). Interest in the field of cannabinoids has been strengthened by the identification and cloning of cannabinoid receptors located in the central nervous system and the peripheral immune organs, and by the discovery of the endogenous cannabinoid ligands. Cannabinoids are also efficacious in animal models of MS. However, there have been only ten published clinical reports on the use of cannabis in MS, involving 78 individuals worldwide, and the results have been equivocal. Researchers encounter a number of difficulties in designing clinical studies that use cannabinoids. From the studies reporting the use of cannabinoids in MS patients with spasticity, the somewhat better designed studies failed to demonstrate objective improvement. Therefore, convincing evidence that cannabinoids are effective in MS is still lacking.