Cannabis research, conceptual image. Dried leaves and flowers of the marijuana plant (Cannabis satvia). Cannabis may be useful medically due to its ability to relieve pain, increase appetite and control muscle spasms. The main active compounds are cannabinoids such as THC (tetrahydrocannabinol). Cannabis shows potential to treat the side-effects of chemotherapy and the symptoms of conditions such as AIDS, multiple sclerosis and chronic pain from nerve damage. In 2005, the Spanish government made the desicion to support the largest trial of medical cannabis ever conducted. The research shall be carried out amongst four hospitals, sixty pharmacies and 1,500 patients in Catalunya.