Definition of St John's wort

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St John's wort: A flowering plant, Hypericum perforatum, also known as Perforate St John's wort, that has long been believed to have medicinal qualities.

There is, in fact, some evidence that St John's wort may possibly be useful in diminishing depression. K Linde and coworkers reviewed 23 published reported trials, including one of 1757 patients, indicating that extracts of St John's wort are more effective than placebo for the treatment of mild to moderately severe depression (British Medical Journal 313:253-8, 1996).

Sun sensitivity, fatigue, stomach upset, and allergic reactions are among the side effects that have been reported in people taking St John's wort.

The powers of this venerable herb were reputed to derive from John the Baptist; red spots on its leaves were said to appear on August 29, the anniversary of his death, representing the blood spilt when St John was beheaded. Others hold that the herb is named for the Knights of St John who used it to treat the wounded in the Crusades.