One of the most distressing symptoms in medicine is the prolonged nausea and vomiting which regularly accompanies treatment with many anti-cancer agents. Of all the potential medicinal uses of cannabinoids, there is most information on their effects in nausea and vomiting caused by anti-cancer drugs. Some investigators have found smoked cannabis to be more effective than oral Tetrahydrocannabinol (THC). This may be because inhaled THC is more readily absorbed than oral THC and also because cannabis contains other substances which enhance the effect of THC. Cannabinoids are undoubtedly effective as anti-emetics in patients with a variety of cancers being treated by a range of anti-cancer drugs which cause vomiting. It is somewhat paradoxical that cannabinoids are reported to be of therapeutic value in neurological disorders associated with spasticity, ataxia, muscle weakness and tremor, since very similar symptoms can be caused by cannabis itself.