Study questions St. John's Wort's effectiveness

In 1998, U.S. sales of St. John's Wort were estimated to be $210 million, according to a previous Duke University study.

DURHAM, North Carolina (CNN) -- St. John's Wort, a popular herbal supplement, is not effective in treating cases of major depression, according to a study released Tuesday.

The study drew immediate fire from supporters of the supplement, who said it is effective in treating mild and moderate cases of depression.

The over-the-counter supplement is widely used to treat depression -- in many cases by patients who don't consult doctors.

In the largest clinical trial to date on the supplement, researchers at Duke University Medical Center measured the effectiveness of the supplement by comparing a group of patients using St. John's Wort to patients being treated with a placebo.

CNN NewsPass VIDEO A new study found that St. John's Wort, a popular herbal supplement used to treat depression, is not as effective as first thought. CNN's Dr. Sanjay Gupta reports (April 10) Play video

The researchers also looked at a control group of patients being treated with the antidepressant sertraline (sold as Zoloft).

The 340 patients, unaware of which treatment they were receiving, were given a dosage three times a day for eight weeks.

The patients were assessed weekly or biweekly and those that responded, at least partially, during the first eight weeks were entered into an 18-week continuation phase.

After eight weeks, improvement was cited in 32 percent of patients treated with a placebo, versus 24 percent of those taking St. John's Wort, according to the study.

Such improvement was cited in 25 percent of those treated with Zoloft, but Dr. Jonathan Davidson -- the lead researcher -- cautioned that the Zoloft was administered in lower than the normal clinical dose, which could account for its relatively low success rate.

The findings were published in this week's Journal of the American Medical Association. It was the second study within a year to question the effectiveness of St. John's Wort.

"Major depression is treatable, but this research suggests that major depression of at least moderate severity should not be treated with St. John's Wort," Davidson said.

Other clinical trials have found St. John's Wort to be as effective as conventional antidepressants in treating mild to moderate depression, according to the National Center for Complementary and Alternative Medicine, part of the National Institutes of Health

And Davidson said St. John's Wort could prove effective for people who suffer from milder forms of depression, noting his study looked only at major depression characterized as moderately severe

Patrick Bridges, vice president of marketing for Abkit Inc. -- the U.S. distributor for one of the makers of St. John's Wort -- called the study "inappropriate."

"The study isn't relevant," Bridges said, pointing out that the supplement is not billed as a treatment for major depression, but is effective in cases of mild to moderate depression.

Davidson said that rather than using over-the-counter treatments, "patients are strongly advised to consult an appropriate health care provider to assess the best treatment for a depressive episode."

He said he believes the popularity of St. John's Wort is because it is so available. Davidson cautioned that just because a product is "natural" does not mean that it is safe.

St. John's Wort has been shown to interact dangerously with medications such as those taken to prevent rejection from organ donation, those used to treat some cardiac conditions, and medications for HIV and AIDS.

According to the National Institute of Mental Health, major depression affects approximately 9.9 million American adults age 18 and older in any given year and is a leading cause of disability in the United States.

In 1998, U.S. sales of St. John's Wort were estimated to be $210 million, according to a previous Duke University study.

The current study was funded by the National Center for Complementary and Alternative Medicine, the National Institute of Mental Health and the Office of Dietary Supplements. All three are divisions within the National Institutes of Health.

The inclusion of the Zoloft control group was to provide a cross-check of the study's validity rather than to test that medication's effectiveness, according to the report.

A spokesman for Pfizer, the maker of Zoloft, said that while the company was happy with the way the study was conducted, it had 10 years of clinical studies that proved the drug worked.

Studies of Zoloft are typically "flexible dosage trials," in which a patient's dosage is adjusted to achieve maximum clinical benefit. The control group in this study was given a set dosage.