Biperiden hydrochloride is a muscarinic receptor (mAChR M) antagonist that displays some selectivity for the mAChR M1 subtype (Ki values are 0.48, 2.4, 3.9, 6.3 and 6.3 nM for mAChR M1, mAChR M4, mAChR M3, mAChR M2 and mAChR M5 receptors, respectively)