The invention relates to a thermoformed pharmaceutical dosage form having a breaking strength of at least 300N, said dosage form comprising - an opioid (A), - a free physiologically acceptable acid (B) in an amount of from 0.001 to 5.0 wt.-%, based on the total weight of the pharmaceutical dosage form, and - a polyalkylene oxide (C) having a weight average molecular weight Mw of at least 200,000 g/mol.本發明係關於一熱成型之藥品劑型,其具有至少300牛頓之破裂強度,所言之劑型包含:- 類鴉片藥劑(A),- 游離型,於生理上可被接受之酸(B),其含量從0.001至5.0個重量百分比,係以該藥品劑型之總重量為依據,及- 聚烯化氧(C),其所具有之重量平均分子量Mw至少為200,000公克/莫耳。