Q: I did go to the Environmental Working Group website you recommended to look at the ingredients in my progesterone cream and noticed that progesterone is listed as a possible carcinogen. What’s that about?
A: Here’s a clear, accurate description of this labeling issue, as explained by the nonprofit group Women in Balance:
“The state of California, under Proposition 65, requires warning labels on consumer products that contain ingredients “known to the state” as posing potential cancer risk. Women in Balance believes that placing a warning label on progesterone cream products is not warranted. We would like to educate consumers about how Proposition 65 came about.
What is California Proposition 65?
California’s Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65 (“Prop 65”), contains a list of over 800 chemicals identified as carcinogens. Prop 65 mandates that warnings be given to consumers of products that contain certain chemicals identified by the state of California as hazardous. Progesterone was added to this list in 1988 based on summaries from the National Toxicology Program (NTP) and the International Agency for Research on Cancer (IARC). Both of these programs only evaluated progesterone given to animals already predisposed to cancer. Progesterone was then given to these high risk animals in very high doses. Also, these animals were given known carcinogens in addition to the high doses of progesterone.
The NTP’s Tenth Report on Carcinogens even acknowledges that “no adequate human studies of the relationship between exposure to progesterone and human cancer have been reported.” Progesterone is a naturally occurring hormone produced by all humans, unlike most of the chemicals listed in Prop 65, which are not naturally present in humans.”
I’d like to add that most of the research originally cited by the NTP to justify adding progesterone to the list of carcinogens was largely based on synthetic progestins—apparently they didn’t realize that progesterone and progestins are very different. Progesterone cream companies that don’t add this label in California become vulnerable to lawsuits from a particularly nasty group of attorneys who are using Prop 65 to make millions of dollars. Meanwhile, there are 799 other chemicals out there, most of which probably do pose a risk of cancer.
If you’d like to read about all the ways that progesterone prevents cancer, please read the book I co-authored with Dr. John Lee and Dr. David Zava, What Your Doctor May Not Tell You about Breast Cancer. Although it was published in 2002, Dr. Zava, myself and others have kept a close eye on progesterone-related research and studies since then, and new evidence comes out monthly supporting everything we put forth in the book. You’ll also find some articles specifically about progesterone and cancer in Vol 3 Issue 1 of the Health Watch.