Hyperforin is one of the principal constituents ientified in St John's wort. Hyperforin is a prenylated phloroglucinol believed to be the main active constituent responsible for its antidepressant effects. Hyperforin has been shown to inhibit the uptake of 5-HT(serotonin), dopamine, noradrenaline, GABA and glutamate. Hyperforin is also thought to be responsible for the induction of the cytochrome P450 enzymes CYP3A4 and CYP2C9 by binding to the Pregnane X Receptor (PXR).