The invention relates to a thermoformed pharmaceutical dosage form having a breaking strength of at least 300 N, said dosage form comprising - a pharmacologically active ingredient (A), - a free physiologically acceptable acid (B) in an amount of from 0.001 wt.-% 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 M w of at least 200,000 g/mol.
