Harvard Mental Health Letter

Update on St. John's wort

June is the legendary birthday of John the Baptist and the month in which St. John's wort (Hypericum perforatum) blooms. Extracts from its flowers have been used for centuries as a painkiller, sedative, and treatment for anxiety and depression. Today, St. John's wort is available by prescription in Europe and over the counter in the United States. Although it is one of the most popular herbal preparations in this country, outselling standard prescription medications for depression, its effectiveness remains in doubt.

Like most plant extracts, St. John's wort contains a mixture of compounds, and its effects are probably due to some combination of these substances; the most important one is called hypericin. Like most antidepressant drugs, St. John's wort usually takes several weeks to work. How it works is not clear — possibly like the selective serotonin reuptake inhibitors (SSRIs), by preventing reabsorption of the neurotransmitter serotonin.

What the studies show

St. John's wort first attracted widespread professional attention in 1996, when a pooled analysis of 30 European clinical trials showed that it was as effective as standard antidepressant medications. In more recent research, the picture has become muddy:

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