Zuclopenthixol-[d4] Succinate Salt is the labelled succinate salt of Zuclopenthixol. Zuclopenthixol is an antagonist at D1 and D2 dopamine receptors. It also has high affinity for alpha1-adrenergic and 5-HT2 receptors, but it has weaker histamine H1 receptor blocking activity, and even lower affinity for muscarinic cholinergic and alpha2-adrenergic receptors. It is the cis-isomer of clopenthixol. It is an antipsychotic drug belonging the thioxanthene class. It was introduced in 1962 by Lundbeck. It has been listed, but is not approved for use in the United States.