Regarding severe depression, NIH chimes in with the university, saying, "Two large studies, one sponsored by NCCAM [the National Center for Complementary and Alternative Medicine], showed that the herb was no more effective than placebo in treating major depression of moderate severity."
Meanwhile, scientists at the Cochrane Collaboration recently evaluated 29 studies on St. John's wort in 5,489 patients. The studies, which were done in a wide range of countries, lasted from four to 12 weeks, and compared the herb with antidepressants and placebos.
The Cochrane group, an international, nonprofit, independent organization dedicated to making up-to-date, accurate information about the effects of health care readily available worldwide, concluded the following: St. John's wort works better than placebos on mild to moderately severe depression and about the same as standard antidepressants.
Interestingly, research on the herb conducted in German-speaking countries had better results than trials conducted in other countries. The Cochrane scientists said that, in the Germanic countries, "these products have a long tradition and are often prescribed by physicians. ... These differences could be due to the inclusion of patients with slightly different types of depression, but it cannot be ruled out that some smaller studies from German-speaking countries were flawed and reported overoptimistic results."