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St. John's Wort

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What is it?

St. John's Wort, known by botanists as Hypercium perforatum, is a five petalled yellow flower which grows wild in much of the world. It was named after John the Baptist because it blooms around his feast day (June 24th). It is used as an antidepressant but studies are currently investigating its use as an anticancer agent and an antiviral agent.

How does it work?

Hypericin is the putative active ingredient. Hypericin has a high affinity for GABA, a chemical transmitter in the brain, the stimulation of which is known to have antidepressant effects. Hypericin has also been shown to stimulate dopamine receptors and inhibit serotonin receptors in the brain. Changes in these chemical transmitters in the brain affect mood.

Is it effective?

Yes! The regimen shown to be effective in clinical trials is 300mg three times a day of an extract standardized to .3% Hypericin. A meta-analysis of 23 randomize controlled trials of St. John's Wort showed that it was equally effective as tricyclic antidepressants in treating depression with significantly fewer side effects.

What is the state of the science?

The first clinical trial in the United States by the National Institutes of Health and the National Institute of Mental Health to determine optimal dosing, long term side effects and efficacy compared to commonly prescribed antidepressants such as fluoxetine hydrochloride was undertaken in 1998. This will be a three year multicenter trial. N-Sights will keep abreast and publish the results as soon as they become available.


Helen Lane, Ph.D., R.D., is the Program Director of the Advanced Human Support Technology at the Johnson Space Center.

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