A new study into the herbal supplement St John's Wort suggests it is not effective as a treatment for depression. Researchers from Duke University Medical Centre in North Carolina found it had no more impact on major depression than a placebo. Dr Jonathan Davidson, director of the Anxiety and Traumatic Stress Program at Duke, said: "Major depression is treatable. But this research suggests that major depression of at least moderate severity should not be treated with St John's Wort."