A plant may be effective in treating mild to moderate depression, according to researchers in Germany performing work for the Cochrane Review.

"Overall, we found that the St. John's wort extracts tested in the trials were superior to placebos and as effective as standard antidepressants, with fewer side effects," said lead researcher Klaus Linde of the Centre for Complementary Medicine.

Extracts of the plant Hypericum perforatum, commonly known as St. John's wort, have long been used in folk medicine to treat depression and sleep disorders, according to a news release on the research. The plant produces a number of different substances that may have anti-depressive properties, but the whole extract is considered to be more effective.

Researchers reviewed 29 trials which together included 5,489 patients with symptoms of major depression. All trials employed the commonly used Hamilton rating scale for depression to assess the severity of depression.

In trials comparing St. John's wort to other remedies, the plant extracts were equally effective and fewer patients dropped out of trials due to adverse effects.

The overall picture is complicated, however, by the fact that the results were more favorable in trials conducted in German-speaking countries, where St. John's extracts have a long tradition and are often prescribed by doctors.

Despite the favorable findings for St. John's wort, researchers were anxious not to make generalizations about the plant's use as an anti-depressant and recommended consulting a doctor in the first instance, especially since extracts can affect the actions of other drugs.