One of the most useful types of study is the systematic review, where researchers combine results from many studies on a single topic. Because reviews include large numbers of participants, many different researchers and institutions, and occur over many years, the results are more robust than any single study.
In this systematic review, researchers included only randomized, double-blind studies of people with major depression who took St. John’s wort extract, standard antidepressant drugs or a placebo for four to 12 weeks. In all, doctors identified 29 studies totaling 5,500 participants. Each study used a common questionnaire called the Hamilton Rating Scale to measure how symptoms changed.
Overall, researchers concluded that, for relieving symptoms of major depression, St. John’s wort is superior to placebo and as effective as standard antidepressants with fewer side effects. Among the findings, in nine of the largest trials, St. John’s wort extract was 28 percent more effective than placebo, and in nine smaller studies, 87 percent more effective. Compared to antidepressants, St. John’s wort extract was just as effective, but those taking St. John’s wort were four times more likely to continue treatment than those taking drugs like Elavil and Mirtazapine and twice as likely to continue treatment compared to drugs like Zoloft and Paxil.
In a study of depression relapse in European Neuropsychopharmacology, researchers followed 700 male and female outpatients, aged 18 to 65, with multiple recurring episodes of major depression. After one week of no treatment, participants took 900 mg of St. John’s wort extract in three 300 mg doses per day for six weeks. Those who responded well to the six-week treatment continued for another 26 weeks taking the same dose of St. John’s wort or a placebo. Participants who did not relapse during the 26-week phase then entered a 52-week phase where doctors reassigned treatment or placebo. Overall compared to placebo, those taking St. John’s wort consistently felt better longer, with more time between episodes of depression and had fewer relapses.