1-(o-Methoxyphenyl)piperazine is a metabolite of drugs bearing a methoxyphenylpiperazine side-chain.

Drugs bearing an o-methoxyphenylpiperazine (oOCH3PP) moiety in the side-chain of their molecule may form oOCH3PP during biotransformation in-vivo in the rat. This has been verified by combined gas chromatography-mass spectrometry of urine from rats given orally a series of relatively new o-methoxyphenylpiperazine-substituted derivatives. The metabolite is reported to be biochemically and pharmacologically active and therefore its formation may have pharmacological significance, at least for derivatives undergoing extensive cleavage of the arylpiperazine side-chain.