The popular herbal extract St. John's wort is more effective at treating the symptoms of depression than any antidepressant drug, and has fewer side effects, researchers from the Centre for Complementary Medicine in Munich have concluded.

"Overall, the St John's Wort extracts tested in the trials were superior to placebo, similarly effective as standard anti-depressants, and had fewer side effects than standard anti-depressants," lead researcher Klaus Linde said.

In a study published by the Cochrane Library, the researchers compiled the results of 29 prior trials, involving a total of 5,489 participants who were randomly assigned either St. John's wort, a placebo, tricylclic antidepressants or selective serotonin reuptake inhibitors (SSRIs) to treat mild to moderately severe depression. All studies were double-blind, meaning that neither patients nor researchers knew what kind of treatment each participant was receiving.

St. John's wort was found to be more effective than a placebo and at least as effective as both tricylics and SSRIs, but with fewer side effects. Patients receiving the herbal treatment were significantly less likely to drop out of studies due to negative side effects than those assigned to take tricyclic antidepressants.

The researchers called their study the most thorough to date, and possibly the first to show that St. John's wort is effective at treating not only mild, but also severe depression (also known as major depression). St. John's wort, known officially as Hypericum perforatum, is a native European perennial herb with distinctive yellow flowers and now grows wild in many parts of the Americas as well. It derives its common name from the tradition of harvesting its flowers on St. John's day (June 24). Also known as Klamath weed or Tipton's weed, the plant has been used for centuries as an herbal remedy for depression and sleeping problems.

In recent years, the popularity of the herbal antidepressant has soared as new concerns continue to emerge over pharmaceutical antidepressants, especially SSRIs. In Germany, doctors regularly prescribe it to children and teenagers. In the United Kingdom, it is currently used by two million people.

SSRIs have been shown to significantly increase the risk of suicide in those under the age of 18, and evidence suggests that they may have a similar effect on adults, as well. Recent evidence has also linked use of the drugs by pregnant women with an elevated risk of oral and heart-related birth defects.

With Western health care systems emphasizing drugs for the treatment of mental illness, however, many doctors feel they have no alternatives but to prescribe tricyclics or SSRIs, in spite of the risk. The new study may lead more doctors to prescribe St. John's wort instead.

Another recent study, conducted by St. James' University Hospital in Leeds, England, found that St. John's wort was the only herbal supplement effective at treating depression, in contrast to cat's claw, ginseng, gingko biloba, liquid tonic and royal jelly.

Researchers remain unsure precisely how St. John's wort works, in part because the plant contains chemicals from at least seven different families. The most favored explanation is that the herb acts much like an SSRI, slowing the rate at which the neurotransmitter serotonin is removed from the brain. The chemical hyperforin is posited by some as the most active chemical agent in the herb, and has been linked to slowed uptake of not only serotonin but also the neurotransmitters dopamine, noradrenaline, GABA and glutamate. St. John's wort extracts from which hyperforin has been removed, however, have still been shown to function as effective antidepressants.