4-(4-Chlorophenyl)-4-piperidinol (CPPO) is one of haloperidol metabolite. Neurotoxicity studies in frogs, which have been used to detect N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) action, showed that CPPO did not mimic the neurotoxicity of MPTP but caused a delayed and persistent freezing action in Rana pipiens frogs. It is proposed that this action may contribute to some of the delayed side-effects associated with haloperidol therapy.

Zuclopenthixol is indicated the management of the manifestations of schizophrenia and other mental illnesses with disturbances in thinking, emotional reactions and behaviour. It is also used to treat the manic phase of manic depressive illness. Zuclopenthixol, a thioxanthene derivative, has high affinity for both dopamine D1 receptors and dopamine D2 receptors. Zuclopenthixol also has high affinity for α1-adrenergic and 5-HT2 receptors. Zuclopenthixol (CLOPIXOL®) is avavilable in the form of tablets and solution for intramuscular injections.