'St John's wort doesn't work'

St John's wort, the herbal supplement for depression, is totally ineffective and may even be dangerous,

Use of the herb has grown in recent years but a study has found it has no more impact than a dummy medicine. Researchers from Duke University Medical Centre in North Carolina, carried out the largest clinical trial of the impact of the herb.

Leading team member Dr Robert Califf said: "As long as these products remain available without unbiased studies, taking them is like playing Russian roulette with your health."

The study appears in the Journal of the American Medical Association.