Doxylamine-d5 succinate is deuterium labeled Doxylamine succinate (HY-A0069A). Doxylamine succinate is a first-generation antihistamine and acts as a histamine H1 receptor antagonist. Doxylamine succinate is orally active, possessing analgesic and hypnotic activities. Doxylamine succinate enhances the activities of CYP2B, CYP2A, CYP3A and thyroxine-glucuronosyltransferase via promoting substrate hydroxylation and thyroxine metabolic pathways. Doxylamine succinate decreases serum thyroxine (T4) level and elevates serum thyroid-stimulating hormone (TSH) level. Doxylamine succinate induces liver enlargement and increases the activities of hepatic microsomal cytochrome P450, cytochrome b5 and NADPH-cytochrome c reductase. Doxylamine succinate can be used for the research of nausea, allergy, insomnia[1][2][3].