Eight years and $36.5 million after Alzheimer's disease researchers from the University of Pittsburgh and elsewhere launched the biggest U.S. study ever of whether ginkgo biloba could help stave off dementia, they got an answer.

It just wasn't the result they wanted.

The Ginkgo Evaluation of Memory Study found adults older than 75 taking the popular herbal extract were just as likely to develop dementia as those ingesting a placebo. In fact, among the 3,069 participants in Pittsburgh and three other locations, those using ginkgo tablets had an even greater likelihood of developing Alzheimer's, although not by a statistically significant difference.

The findings, published in the Journal of the American Medical Association today, have apparent use in ruling out one of the often-touted potential tools against the dreaded disease. That's not as valuable, however, as what they had hoped.

"Of course I'm disappointed. We're all terrifically disappointed," said Dr. Steven DeKosky, a neurologist who headed the study and left Pitt this year to become dean at the University of Virginia School of Medicine. "The reason I do research in the disease is I want to find ways to beat it."

The federal government's National Center for Complementary and Alternative Medicine invested $25.3 million as the primary funder of the multicenter trial, in which participants with no history of dementia were assessed every six months for signs of developing it.

Smaller studies had suggested the antioxidant qualities of ginkgo, a relatively low-cost herbal supplement, might counter memory loss in some who already have Alzheimer's -- much like more expensive pharmaceutical drugs.

Dr. DeKosky said it would have been a major finding if those taking twice-daily doses of 120 milligrams of ginkgo developed Alzheimer's at a rate 20 percent to 30 percent below that of the other study participants. Instead, 277 members of the ginkgo group -- or 18 percent -- and 246 of the placebo group -- 16 percent -- were diagnosed with the cognitive disease over six years of study.

Generally, about 4 percent of the population 75 and older will develop the disease each year.

A similar study of ginkgo's value is being held in Europe, with results anticipated in a year or two, but the thoroughness of the DeKosky-headed trial would make it surprising to see a different outcome, said Dr. Richard Nahin, acting director of extramural research for the national alternative medicine center.

"It's clear, not ambiguous at all," he said. "One potential medical product to help prevent dementia is just no longer available."

Plenty of people are still likely to take ginkgo as a health supplement, for various reasons. U.S. consumers spent $107 million on it last year, according to Nutrition Business Journal estimates. And its advocates expressed skepticism of the study's findings.

The Natural Products Association issued a statement saying people younger than 75 need to be evaluated while taking ginkgo, because its preventive benefits could take longer to show up than is evident with the old age group in the study.

And the American Botanical Council said it wasn't willing to dismiss other research that has showed "the safety and efficacy of gingko extract for both cognitive function and improved circulation."

The national Alzheimer's Association has never been sufficiently impressed to recommend ginkgo as a way of preventing or countering the disease. Dr. William Theis, the association's vice president of medical and scientific relations, said the data "was always questionable."

"This sort of puts a period on that discussion," he said. "People spending lots of money on ginkgo can find other ways to use that money."

No dangerous side effects were noted among the ginkgo users, Dr. DeKosky said, meaning it is safe for use by those who still want to. As far as whether the findings are conclusive, "disproving the negative is always impossible," said the neurologist, who headed Pitt's Alzheimer's Disease Research Center and has been recognized as a leading medical spokesman for the Alzheimer's Association.

"Can I prove it has no effects? No. What I can say is that for people over 75, taking a high dosage of this didn't show a positive effect in the population," Dr. DeKosky stressed. "If people want to believe in it, I don't have a strong reason to say you should stop."

In addition to Pitt, participants in the study were chosen and assessed through Johns Hopkins University, the University of California-Davis and Wake Forest University.