Studies concluding that St. John's wort (Hypericum perforatum) is an effective antidepressant can be challenged due to questionable methodology. We attempt to correct this by a meta-analysis utilizing only well-defined clinical trials. Controlled, double-blind studies using strictly defined depression criteria were analyzed by the rate of change of depression and by the number of "treatment responders." Rates of side effects and dropouts were also analyzed. Hypericum was 1.5 times more likely to result in an antidepressant response than placebo and was equivalent to tricyclic antidepressants (TCAs). The meta-analysis also showed that there was a higher dropout rate in the TCA group and that the TCAs were nearly twice as likely to cause side effects, including those more severe than hypericum. Hypericum perforatum was more effective than placebo and similar in effectiveness to low-dose TCAs in the short-term treatment of mild to moderately severe depression. However, design problems in existing studies prevent definitively concluding that St. John's wort is an effective antidepressant.