"It's not a manufactured progesterone," Peterson said. "I think they have their facts wrong. One of our marketing tactics has been that it is not a modified or manufactured progesterone but a natural, soy-based progesterone."

Progesterone is a critical female hormone. It helps regulate menstruation in pre-menopausal women and is used with estrogen to treat post-menopausal women with hormone imbalances.

The hormone is at the center of several controversies. Some scientists believe it helps prevent miscarriages in a select group of high-risk women during the first trimester of pregnancy. Others believe it helps minimize preterm delivery in a small high-risk group of pregnant women.

Dr. Elliott Brinton, an expert in post-menopause estrogen and progesterone treatment at the University of Utah, said additional questions surround the effectiveness of plant progesterone in human treatments.

"The evidence of effectiveness of plant hormones in humans is controversial and incomplete. If you look carefully at the science, you'll see the effectiveness of human hormones to plant hormones is not a 1-to-1 ratio. A lot of women believe soy estrogens or other plant-derived estrogens give them a lot of relief, and I wouldn't deny that is true, but if you look at studies, they are fairly ineffective. An individual woman might have a good effect, but across the board, there is little benefit."

Brinton said the CWLC's complaint raises important issues.

"Taking progestins along with the estrogen after menopause can increase the risk of breast cancer," he said. "There is some basis for the state of California to say there is a relationship to cancer. The question is, does it have any relationship in these products? I don't know.

"It's a very sticky issue. I don't know where the truth lies here, but I can tell you I am frequently concerned when I see the claims made by the manufacturers of supplements. Many of them are taking one little snippet of science and adding it to anecdotes that a product helped a few people and then saying they have cures."

Carrick said the CWLC has settled with six companies. It is asking companies to pay $20 per unit sold over the past four years. It also wants companies to place a cancer warning on labels, advise consumers to use the products only under a physician's care and to abandon any outrageous claims.

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E-mail: twalch@desnews.com