The use of the cannabis plant for various medical indications by cancer patients has been rising significantly in the past few years in several European countries, the US and Israel. The increase in use comes from public demand for the most part, and not due to a scientific basis. Cannabis chemistry is complex, and the isolation and extraction of the active ingredient remain difficult. The active agent in cannabis is unique among psychoactive plant materials, as it contains no nitrogen and, thus, is not an alkaloid. Alongside inconclusive evidence of increased risks of lung and head and neck cancers from prolonged smoking of the plant produce, laboratory evidence of the anti-cancer effects of plant components exists, but with no clinical research in this direction. The beneficial effects of treatment with the plant, or treatment with medicine produced from its components, are related to symptoms of the disease: pain, nausea and vomiting, loss of appetite and weight loss. The clinical evidence of the efficacy of cannabis for these indications is only partial. However, recent scientific data from studies with THC and cannabidiol combinations report the first clinical indication of cancer-related pain relief. The difficulties of performing research into products that are not medicinal, such as cannabis, have not allowed a true study of the cannabis plant extract although, from the public point of view, such studies are greatly desirable.