Hypericin is a substance derived from the herb Hypericum perforatum, commonly known as St John’s wort or goatweed.

Herbal preparations of St John’s wort at a concentration of 0.14% are available in most health food shops. They are sold under the names Hyperforat and Psychotonin. The extract contains at least ten substances including hypericin, hyperforin, pseudohypericin, xanthenes, monoterpenes, beta-sitosterol, quercetin and catechin. A stronger preparation containing 4.4% is available from buyers’ clubs under the trade name HY10 or HY4.

Researchers have also developed a synthetic version called VIMRxyn, which is produced by the company VIMRx.

St Johns wort is an effective treatment for mild to moderate depression. A review of eight randomised controlled trials of found that St John’s wort is more effective than placebo in treating mild to moderate depression^[1]. Although hypericin was thought to be the active ingredient in St John’s wort, recent test tube evidence suggests that other constituents of this plant may be responsible for its psychological effects^[2].

Hypericin was tested as an anti-HIV drug, but studies found only weak anti-HIV effects that were not of benefit in HIV-positive patients^[3][4]. However, a research group has recently identified a protein extracted from St John’s wort called p27^SJ that has anti-HIV properties and may form the basis of future drug development^[5].

Side-effects of St John’s wort are rare. One study found that only 2% people who took the extract to experience reported side-effects, such as nausea, rash, fatigue, restlessness and sensitivity to heat or cold.

Since it enhances the activity of the cytochrome P450 system, St John’s wort reduces levels of all the protease inhibitors and non-nucleoside reverse transcriptase inhibitors (NNRTIs)^[6][7]. Patients taking any of these drugs should not take St John’s wort, as it can cause a reduction in anti-HIV effects, putting patients at risk of drug resistance and treatment failure. These effects can persist for up to two weeks after St John’s wort treatment is stopped.

St John’s wort should also be avoided by patients taking other medications metabolised via the same route.