PROVO — Two Utah companies say their progesterone creams enhance female sex drive or reduce food cravings in women over 40, but a California group lists both as dangerous and is threatening to sue.

The California Women's Law Center and its executive director, Katherine Buckland, filed a notice last month that it would sue in 60 days if the companies don't stop selling the products or change their labels to show that progesterone can cause cancer and should only be used with a physician's advice.

Provo-based Tahitian Noni says its product, Tahiti Trim Plan 40 Body Balance Cream, cuts cravings in women over 40 who want to lose weight. Company spokesman Andre Peterson said the product is safe.

"Tahitian Noni International has received notice about the lawsuit from the woman in California. We are currently looking into the situation but at the current we do not consider her demands to be meritorious."

Another Utah County firm, Klein-Becker, says its Testrogel Acute Transfer Androgenic Gel enhances sexual appetite in women. Some Internet sales sites say it also enhances sexual energy and performance in both genders. A message left for company executives was not immediately returned after business hours Friday evening.

Both creams are designed to be applied to the inner arm, thigh or chest area, or another place where skin is thin, so that the progesterone is quickly absorbed into the bloodstream.

The California Women's Law Center (CWLC) has filed suit against more than 50 companies that make similar products with testosterone or progesterone. The groups sent notice to Tahitian Noni, Klein-Becker and 32 other companies last month that they had 60 days to respond or they, too, would be sued.

A key issue is the difference between natural and synthetic progesterone. Natural progesterone is considered safe, while synthetic progesterone can be dangerous.

A small dab of the hormone creams, applied to the skin, can deliver high doses of progesterone quickly into the blood system.

"These are not minor exposures," said Roger Lane Carrick, an attorney representing the CWLC. "Someone using these products on a daily basis is having major exposures. These companies dress up their products as natural, coming from yams. There's no such thing as a naturally occurring progesterone."

That drew a strong reaction from Tahitian Noni's Peterson, who agreed that synthetic progesterone can be dangerous but said the progesterone in "Tahiti Trim" is natural.

"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.