St. John's wort is a herb that's been used for centuries to treat nervous conditions. But what do we really know about it?

"It's probably the best researched of any of the herbals that are currently available to people today," said Dr. John Swartzberg is head of the editorial board at the UC Berkeley Wellness Letter.

"There's enough data to say that we really know that for people with moderate to mild depression it appears to help, probably as well as many of the antidepressants that are available," Schwartzberg said.

And it may have fewer side effects than some prescription anti-depressants.

There is no evidence St. John's wort can treat severe or long-term depression.

Because it's a powerful drug, you should not take St. John's wort without talking to your doctor first.

"And it does have influence on how other drugs that you take are metabolized in your body, so it could have some significant effects with other medications you may be taking," Schwartzberg said.

One more caution: there is no data on the long-term safety of taking St. John's wort, so pregnant or nursing women should not take it.

More Information:

National Center for Complementary and Alternative Medicine