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CORVALLIS, Ore. - The popular dietary supplement ginseng is purported to improve one's mood and all-around vigor, but a new study published today in the Journal of the American Dietetic Association suggests that ginseng has little if any effect on psychological health.

The study, conducted by researchers at Oregon State University and Wayne State University, is one of the most extensive peer-reviewed studies of ginseng ever conducted.

"Ginseng is being marketed to relatively healthy young people as a way to feel even better - a kind of yuppie supplement," said Bradley J. Cardinal, an associate professor in the College of Health and Human Performance at Oregon State. "We found it had no real effect on mood at all. It certainly did not live up to some of its over-enthusiastic marketing claims."

Among the claims, the authors say, were that ginseng enhances mood, leads to positive well-being, and generally makes you feel better. Marketing ploys used to push ginseng promoted its use by astronauts and professional athletes, and claimed it did everything from easing childbirth to working as an aphrodisiac.

The study by Cardinal and Hermann J. Engels of Wayne State University focused only on the alleged psychological properties of ginseng. The researchers gave a regular, 200-mg daily dose of ginseng to one group of volunteers for eight weeks. A second group received a double dose of 400-mg daily; the third group received a sugar pill. None of the individuals knew what they were taking.

At the end of the eight-week period, the researchers measured the effects of the supplements on the volunteers' "total mood disturbance" using a 65-question "Profile of Mood States" inventory. They used the 20-item "Positive and Negative Affect Scale," or PANAS, to target potential positive and negative impacts more specifically. PANAS, commonly used by psychologists and counselors, uses established positive adjectives, such as "active," "alert" and "enthusiastic" and negative adjectives, including "irritable," "jittery" and nervous," to evaluate feelings.

To eliminate bias, the researchers evaluated the tests without initially knowing which subjects were taking ginseng and which were taking placebos. They compared the results with a baseline survey of the volunteers taken just prior to the study.

They found no significant difference among the three groups.

"What these findings on psychological effect do is extend earlier research from our lab that examined physiological outcomes of ginseng," said Wayne State University's Engels. "Our previous research found, using a controlled physical exercise stress test, that ginseng had no effects when given to normal, healthy adults."

In this latest research, the group taking 200-mg of ginseng experienced a 2.5 percent increase in positive feelings during the eight weeks, but the group taking a placebo had a greater increase, 5.0 percent. The largest gain in positive feelings, 7.7 percent, went to the group taking 400-mg of ginseng, but all of those numbers were within a statistical margin of error, making the differences insignificant, the researchers say.

Categories of negative feelings and "total mood disturbance" were even flatter across the board. The placebo group experienced the most noticeable change in negative feelings, a 2 percent increase compared to 0.5 percent for the other two groups.

Cardinal said the most important category was Total Mood Disturbance, because it looked at the broad spectrum of mood enhancement experienced by the volunteers. The 200-mg group experienced a greater increase, 1.8 percent, than the 400-mg group, which increased only 0.3 percent. The placebo group was in between with a 1 percent increase.

"Statistically, there really was no difference between the groups that took ginseng, and the group that didn't," Cardinal said. "It is still possible that ginseng may have an effect on certain individuals, or certain populations, such as the sick and the elderly. But higher doses also may bring on unwanted side effects. These are issues that need to be clarified with additional well-controlled studies in the future."

Cardinal says the researchers set out to improve upon 27 other published studies on ginseng they found in the literature. Their study used more volunteers (83) for a longer duration than almost all the other studies, and they even sent their ginseng to an independent laboratory to ensure that it was of high quality.

Their double-blind, placebo-controlled study was designed to eliminate bias by both the volunteers and the researchers themselves. "The bottom line," Cardinal said, "is that ginseng doesn't seem to do much to enhance the psychological well-being of normal, healthy adults."