Trihexyphenidyl-d5 is deuterium labeled Trihexyphenidyl (HY-B1277A). Trihexyphenidyl is a selective and orally active M1 muscarinic receptor antagonist with an IC50 of 3.7 nM for rat cerebral cortex M1 muscarinic receptors. Trihexyphenidyl modulates cholinergic activity, countering acetylcholine supersensitivity in neural pathways. Trihexyphenidyl improves movement disorder, inhibits McN-A-343 (HY-107648)-induced pressor responses, vagally-induced bradycardia and vasodilatation. Trihexyphenidyl can be used for the research of Parkinsons disease.[1][2][3].