Chicago ? The first scientific tests of some popular alternative medicine products hint that American ginseng might lessen cancer fatigue and that flaxseed might slow the growth of prostate tumors.

But a big study proved shark cartilage worthless against lung cancer, and doctors said people should not take it.

The research was reported Saturday at an American Society of Clinical Oncology conference.

The ginseng and flaxseed studies are small and preliminary, and specialists warned against making too much of them because the substances tested are not the same as what consumers find on store shelves.

But the results suggest that some herbal remedies eventually may find niches for treating specific cancers, symptoms or side effects. Americans spend millions on these products, which are not approved by the federal Food and Drug Administration, even though no good studies confirm the benefits they tout.

“One of the most common things patients ask me is about these things they have snookered away in their purses” and medicine chests, said Dr. Bruce Cheson, a cancer specialist at Georgetown University Hospital. “They’ll come in with big bags of this stuff.”

Some “natural” remedies such as laetrile or high doses vitamin C proved not helpful and even harmful for cancer patients once they were scientifically studied, he noted. Some keep chemotherapy from working as it should.

“Just because it is a vitamin or a leafy green does not ensure it does not have some harmful effects,” Cheson said.

Herbal products vary widely in their purity and the amount and type of active ingredients. These three federally funded studies used standardized compounds so they could say with some certainty whether they have any effect.

The shark cartilage study was done because Congress ordered it. Some very small early studies suggested high doses of it might extend survival of people with advanced cases of non-small cell lung cancer, the most common form of the disease.

Dr. Charles Lu of the University of Texas M.D. Anderson Cancer Center in Houston tested Neovastat, a shark cartilage liquid extract that the Canadian company Aeterna-Zentaris was trying to develop as a regular pharmaceutical product.