Crystalline salts of 7,8-Didehydro-4,5 alpha-epoxy-17-methylmorphinan-3,6 alpha-diol sulfate(2:1), i.e. of morphine sulphate, are disclosed and four polymorphic forms of these salts are reported. The invention further relates to a pharmaceutical composition comprising an amount of such a salt and such a salt as a medicament and for the treatment and/or prevention of pain.
