Studies suggest that St. John's wort is of minimal benefit in treating major depression. A study cofunded by the National Center for Complementary and Alternative Medicine (NCCAM) found that St. John's wort was no more effective than placebo in treating major depression of moderate severity. There is some scientific evidence that St. John's wort is useful for milder forms of depression.

What the Science Says About St. John's Wort for Depression

Scientific evidence regarding the effectiveness of St. John's wort for depression is inconsistent. An analysis of the results of 37 clinical trials concluded that St. John's wort may have only minimal beneficial effects on major depression. However, the analysis also found that St. John's wort may benefit people with minor depression; these benefits may be similar to those from standard antidepressants. Overall, St. John's wort appeared to produce fewer side effects than some standard antidepressants.
One of the studies included in the analysis was cofunded by NCCAM and two other components of the National Institutes of Health (NIH)—the National Institute of Mental Health and the Office of Dietary Supplements. This study found that St. John's wort was no more effective than placebo in treating major depression of moderate severity. However, the antidepressant sertraline, used in one arm of the study, also showed little difference from placebo.