Twenty-five controlled clinical studies completed prior to 1993 involved 1,592 people who took between 300 and 900 mg of an extract of St.-John's-wort tops for two to sixteen weeks. Fifteen of the studies were placebo-controlled; the other ten compared preparations that contained St.-John's-wort with preparations that did not. Unfortunately, many of the studies conducted between 1979 and 1989 included preparations containing both St.-John's-wort and valerian, an herb that is often used as a mild sedative and sleep aid. Although the preparations were beneficial and produced few or no side effects, the mix made it impossible to attribute effects to one herb or the other. Credible clinical studies on St.-John's-wort alone have occurred only recently.

In 1994, a randomized, placebo-controlled, double-blind study--the most rigorous kind of study--by a psychiatrist, an internist, and a general practitioner in Austria evaluated the effect of St.-John's-wort on 105 outpatients diagnosed with mild to moderate depression or with temporary depressive moods. The patients received 300 mg of either St.-John's-wort extract (standardized to 0.9 mg hypericin) or a placebo three times a day for four weeks. Sixty-seven percent of those taking St.-John's-wort and 28 percent of those taking the placebo showed improvement. Those taking the extract felt significantly less sad, hopeless, helpless, and useless, were less fearful, and slept better. Side effects, compared with those caused by synthetic antidepressants, were of minor significance. The authors deemed St.-John's-wort to be safe and effective for mild to moderate forms of depression. However, they cautioned that it is not suitable for more serious conditions such as manic-depressive disorder.

More evidence
Generally speaking, the results of one study only point to the need for more studies. The safety and effectiveness of a substance are not confirmed until well-designed studies have been repeated with a large number of subjects and with similar outcomes.

In 1995, a researcher at the University of Exeter in England evaluated eighteen clinical studies of St.-John's-wort preparations used to treat depression, fourteen using a placebo for comparison and four using standard antidepressive drugs. He found that eight of the placebo-controlled studies and three of the others met acceptable standards of research design. He then evaluated the studies, concluding that St.-John's-wort extract was superior to a placebo and as effective as standard medications in alleviating symptoms of depression, with fewer adverse reactions than standard medications.

Caveats
St.-John's-wort should not be mixed with synthetic antidepressants. Because it may inhibit MAO, taking it with selective serotonin reuptake inhibitors such as Prozac could cause serious health damage.

Additionally, although side effects have not been reported in the clinical studies, range animals eating the plant and then standing in bright sunlight have experienced sunburn or blindness from photosensitization.

Depression is a condition that requires professional medical diagnosis and treatment. If you are taking or contemplating taking St.-John's-wort, this treatment option should be discussed with your health-care provider, especially if he or she has prescribed other drug therapies.

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