A pharmaceutical dosage form having a breaking strength of at least 300 N, said dosage form comprising: an opioid (A) selected from Oxymorphone, Oxycodone, Tapentadol, Hydromorphone, Hydrocodone, Morphine, and physiologically acceptable salts thereof; wherein the weight content of the opioid (A) is from 5.0 to 35 wt.-%; an anionic polysaccharide (B) selected from croscarmellose, carmellose, crosslinked carboxymethyl starch, carboxymethyl starch, and physiologically acceptable salts thereof; wherein the weight content of the anionic polysaccharide (B) is within from 5.0 to 35 wt.-%; and a polyalkylene oxide (C) having a weight average molecular weight of at least 200,000 g/mol; wherein the weight content of the polyalkylene oxide (C) is from 20 to 80 wt.-%; wherein all wt.-%'s are based on a total weight of the dosage form, and the opioid (A) is present in a controlled-release matrix comprising the anionic polysaccharide (B) and the polyalkylene oxide (C).