Cannabis produces its therapeutic effects thanks to its action in the endogenous cannabinoid system. The evidence of the medical effects of cannabis is nowadays unquestionable. Still, in most of the countries the medical users have to turn to self-medication because marihuana is not accepted as a medicine. In this talk I will review the medical basis of the therapeutic effects of cannabis and will will review the international researches that have studied patients who self-medicate with cannabis. I will also explain the sociopolitical situation regarding medical marihuana in Spain.