Harmalol hydrochloride (Harmidol hydrochloride) is a β-carboline alkaloid that can be extracted from the seeds of Peganum harmala L. Harmalol hydrochloride is the major metabolite of Harmaline and significantly inhibits dioxin-mediated induction of CYP1A1 at both transcriptional and post-translational levels. Harmalol hydrochloride showed vasorelaxant activity in isolated rat thoracic aortic preparations preconstricted with phenylephrine or KCl. Harmalol hydrochloride has antioxidant activity.