An injectable pharmaceutical composition includes a solution of 3-acyl-buprenorphine, or a pharmaceutically acceptable salt thereof, in a biocompatible organic solvent, wherein the injectable pharmaceutical composition exhibits a steady release profile lasting over one week when injected into a patient. The acyl group is an alkylcarbonyl group, and an alkyl portion of the alkylcarbonyl group is a straight-chain, branched-chain, having 1-20 carbon atoms. The biocompatible organic solvent is N-methyl-2-pyrrolidone, ethyl acetate, ethanol, butanol, 2-butanol, isobutanol, ispropanol, glycerin, benzyl benzoate, dimethyl sulfoxide, N,N-dimethylacetamide, propylene glycol, dimethyl glycol, benzyl alcohol, or a combination of two or more thereof.一種可注射醫藥組成物，包含溶於生物相容性有機溶劑中的3-醯基-丁基原啡因或其醫藥上可接受之鹽的溶液，其中，當注射該可注射醫藥組成物至病患體內，該可注射醫藥組成物呈現穩定的釋放曲線持續一週以上。該醯基包含烷羰基，且該烷羰基的烷基部分具有1-20個碳原子的直鏈或支鏈。該生物相容性有機溶劑係選自由下列所組成之群組：N-甲基-2-吡咯烷酮、乙酸乙酯、乙醇、丁醇、2-丁醇、異丁醇、異丙醇、甘油、苯甲酸芐酯、二甲亞碸、N,N-二甲基乙醯胺、丙二醇、二甲基乙二醇、苯甲醇，或是其二種或二種以上的組合。
