The invention relates to a novel sustained release pharmaceutical formulation adapted for administration by injection containing the compound 7&agr;-[9-(4,4,5,5,5-pentafluoropentylsulphinyl)nonyl]oestra-1,3,5(10)-triene-3,17&bgr;-diol, more particularly to a formulation adapted for administration by injection containing the compound 7&agr;-[9-(4,4,5,5,5-pentafluoropentylsulphinyl)nonyl]oestra-1,3,5(10)-triene-3,17&bgr;-diol in solution in a ricinoleate vehicle which additionally comprises at least one alcohol and a non-aqueous ester solvent which is miscible in the ricinoleate vehicle.