Clopenthixol is a racemic mixture of cis and transisomers. Zuclopenthixol, the pure cis isomer, was later introduced by Lundbeck in 1962, and has been much more widely used. Both drugs are equally effective as antipsychotics and have similar adverse effect profiles, but clopenthixol is half as active on a milligram-to-milligram basis and appears to produce more sedation in comparison.
Clopenthixol is not approved for use in the United States.