The present invention provides a transdermal delivery system comprising (R)-dihydroetorphine, or a salt, hydrate or derivative thereof, wherein said system has a rapid onset of (R)-dihydroetorphine plasma concentration characterised by the mean in vivo plasma concentration of (R)-dihydroetorphine achieving at least 50 % of its Cmax in less than 20 hours, preferably in less than 18 hours and more preferably in less than 12 hours, after application of the system to the skin of a human subject, e.g. when based on the mean plasma concentration versus time curve.本發明提供一種經皮傳遞系統，其包含(R)-二氫埃托啡((R)-dihydroetorphine)或其鹽、水合物或衍生物，其中該系統具有(R)-二氫埃托啡之平均活體內血漿濃度之快速起始，其特徵在於(R)-二氫埃托啡血漿濃度在向人類個體之皮膚施用該系統之後小於20小時內、較佳在小於18小時內且更佳在小於12小時內(例如當基於平均血漿濃度相對於時間曲線時)達至其Cmax之至少50%。
