The report warns a lack of specialist care may see sufferers seek herbalist or homeopathic treatment.

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But you also have people who specialise purely in the physical illnesses, known as a herbalist, inyanga in Zulu.

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The ancient Persian king Xerxes noted that eating the leaves improved his soldiers' vigor, while the Elizabethan herbalist John Gerard prescribed the plant for restoring the bloom to ladies' cheeks.

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But Dr Ann Walker, senior lecturer in human nutrition at the University of Reading and a qualified medical herbalist, said the findings would make little difference to the average St John's wort user.

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