By Nancy A. Melville,HealthSCOUT Reporter

SATURDAY, Sept. 23 (HealthSCOUT) -- St. John's wort -- the plant that many swear helps ward off depression -- seems to have its own way of dealing with stress.

When attacked by insects, an active ingredient in the plant known as hypericin significantly increases, say researchers with Cornell University and the U.S. Department of Agriculture. That makes the plant's medicinal value even more potent, they say.

"It appears to increase its own chemical arsenal to ward off attack from predators," says Donna M. Gibson, a USDA plant physiologist and adjunct professor of plant pathology at Cornell.

Gibson and her colleagues made the discovery after devising a unique method to measure individual components of the plant. The system enabled them to see that wild populations of St. John's wort that had been exposed to stress, particularly attacks from insects, had increased levels of hypericin. The findings were presented at the annual meeting last month of the American Phytopathological Society in New Orleans.

In St. John's wort sold over-the-counter, the level of hypericin is measured to determine the potency of the product, Gibson says. But it's still not clear whether hypericin is the only active ingredient responsible for the benefits of St. John's wort as an antidepressant, she says.

"It hasn't been totally nailed down," Gibson says. "It may be that the whole extract of St. John's wort works because of a number of compounds that are present."

The researchers are continuing to examine things that happen to St. John's wort before it's harvested that could play a role in chemical differences in the plant, Gibson says. These include such factors as light, moisture, altitude and latitude, the development stage of the plant when it's harvested as well as any harvesting and handling practices that might affect its quality.

St. John's wort typically is gathered as a weedy species in the Western United States, but some is being grown commercially in the Pacific Northwest. It also is found along roadways and in fields in the Eastern United States.

Although widely prescribed in Germany to treat depression and anxiety, St. John's wort is not considered a proven therapy for clinical depression in the United States and, therefore, generally is not recommended by mental health professionals.

According to Jeremy Kirsch, a psychologist and senior director for clinical education for the National Mental Health Association, concerns ranging from side effects to conflicts with other medications cause many experts to shy away from recommending it.

"This is not an inert substance," Kirsch says. "It can have many side effects, including dizziness, fatigue and gastrointestinal problems, and can cause problems when taken with other medications, ranging from HIV and cancer drugs to birth control pills and cholesterol-lowering medications."

"So you definitely don't want to go into this without talking to your doctor first," he says.

(From Yahoo!)