Cannabis research, conceptual image. The marijuana plant (Cannabis satvia) 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 including AIDS, multiple sclerosis and chronic pain from nerve damage. In 2005, the Spanish government made the decision to support the most wide-ranging trial of medical cannabis ever conducted. The trial will involve four hospitals, sixty pharmacies and 1,500 patients from Catalunya.