Does Progesterone Cause Cancer?
07 Jul 2015

Does Progesterone Cause Cancer?

ProgesteronePic320Many people, including regulatory agencies and members of the medical community, make the mistake of thinking that progesterone and synthetic progestins have the same potential for adverse effects. This erroneous thinking is the root of women’s concerns that progesterone causes cancer. It’s also why some states require labeling on progesterone that suggests that natural progesterone products may increase the risk of cancer.

What Does Progesterone Do?

One of progesterone’s most important functions in the body is to help women maintain pregnancy. But it’s not just about baby-making. There are many research studies that show the protective role progesterone plays in the body. It protects against hypertension, lowers blood fats, protects nerves, and prevents coronary hyperactivity (a sign of coronary artery disease) and helps with hot flashes, night sweats, insomnia, and anxiety. There is also evidence that is may be protective against cancer.

There is NO evidence that it increases the risk of breast cancer.

What Does the Data Show?

If you look at the evidence, it’s no wonder there’s confusion.

We know that estrogen replacement (HRT) given without progesterone to women who still have a uterus causes endometrial cancer. Studies published in 1995 found that women who had been exposed to HRT for longer than 5 years had a 32% increased risk of getting breast cancer. If the estrogen was combined with a progestin, it went up to 41%, and for those women who were post-menopausal the risk went up to 71%, while the risk of getting ovarian cancer went up by 72%.

Then in 2002, all hell broke loose. The huge Women’s Health Initiative study was stopped early when the data showed an increase in breast cancer, heart disease, blood clots, and strokes in women who were given traditional HRT. As a result, millions of women were thrown into hormone hell when they were abruptly taken off the drugs by their doctors.

In this study, women were given synthetic estrogen (conjugated equine estrogen) PLUS synthetic progestin (medroxyprogesterone), synthetic estrogen alone (for women who had hysterectomies), or placebo (sugar pill).  Bio-identical progesterone was NOT studied.

The results showed that women in the two-drug group were 24% more likely to develop breast cancer than women in the placebo group. However, women in the estrogen-alone group did NOT have an increased risk (and in fact the, the trend was toward reduced risk). Further subanalysis showed that the SYNTHETIC PROGESTIN was actually the culprit causing the increased breast cancer risk.

Progestin ≠ Progesterone

The medical community has lumped PROGESTERONE into the category of PROGESTINS. Progesterone is chemically identical to the hormone made by your body. PROGESTIN is not chemically identical and may have many side effects such as acne, breast pain, nausea, weight gain, headaches, and irregular periods. Synthetic progestins are found in IUDs, implants, and oral contraceptives.

Bio-identical progesterone is made from a compound found in wild yams (diosgenin). This compound is altered in the lab to be identical to what your body produces. Your body cannot make this conversion on its own, so wild yam cream is not effective. Bio-identical products are available in creams, oils and oral capsules. Creams and oils are available over-the-counter, but oral preparations require a prescription.

What If I’ve had Breast Cancer?

In his book “What Your Doctor May Not Tell You about Menopause”, Dr. John Lee (a pioneer in the study of progesterone) discusses the cancer-protective benefits of progesterone. He refers to various studies; one over a 20-year period which reported a 5.4 times likelihood of breast cancer developing in women with low progesterone levels. He concludes that “the evidence is strong that unopposed estradiol and estrone are carcinogenic for breasts, and both progesterone and estriol, the two major hormones throughout pregnancy, are protective against breast cancer.”

I am not aware of any large-scale clinical trials looking specifically at progesterone use in patients who have had hormone-sensitive cancers. As with many therapies, it’s important to assess risk vs. benefit (including quality of life issues). Any woman who has a history of cancer should discuss the use of any hormonal therapy with her care team.


About Dr. Anna

Dr. Anna Garrett is a pharmacist and menopause expert who helps women who are struggling with symptoms of perimenopause and menopause find natural hormone balancing solutions so they can rock their mojo through midlife and beyond. But her clients would tell you that her real gift is helping them reclaim pieces of themselves they thought were gone forever.

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  1. […] An extremely important takeaway point is that PROGESTERONE and PROGESTINS are NOT the same thing. The medical community tends to lump progesterone into the progestin category, but they work very differently in the body. Progesterone is calming and affects your brain in addition to protecting your uterus from the effects of estrogen. Synthetics have no calming effects and are associated with a number of side effects. Progesterone DOES NOT raise cancer risk, and has not been associated with an increased risk of blood clots or stroke. You can read more about that here. […]

  2. Thank you for this write up, my Naturalistic physician wrote the prescription for Progesterone 50mg caps, however my MD would not sustain the prescription and stated it causes cancer.

    I started taken them again through my Naturalistic physician, but got scared. I benefited so much when I took it in the past, weight loss, lower by blood sugar etc., and now ready to take it again. I hope I do not get Cancer from it. Thank you

    • Cecelia,

      As stated, Progesterone is a bio-identical which means it mimics your own hormone. It’s progestins that you need to steer clear of…they are the ones which cause cancer.I suggest that you go back to your naturalistic doctor and get back on Progesterone.

  3. I’m 52 and had partial hysterectomy in 2010 and started on different estrogen medications but they ALL would cause my face to break out in large painful bumps so eventually I was put on the estrogen patch 0.1 mg one x a week. I have tried to stop the patch but after 2 days of being with out a patch my face breaks out in large painful bumps and I just get to be a emotional wreck. What can I ttake in place of it to control the symptoms. Does progesterone do this. My physician and gynecologist are of no help. And there are no naturopaths in my area. Thank you for your help!!

    • Correct me if I’m wrong, but it sounds like you do OK with the patch. Why do you want to stop it? Adding progesterone may help balance things out. Sounds like your androgens (testosterone and/or DHEA) are out of balance with other hormones. But I couldn’t say for sure without seeing test levels.

      • Dana peard Says: January 29, 2018 at 9:12 am

        I just had a complete hysterectomy a few weeks ago. I am scared to take any hormone replacement. My gyno explained it to me and it sounds good. She is great! I just am so scared to get cancer or have a heart attack. She explain my risk are higher of those two wirh out taking anything. I dont wanr to try and break it down because i do forget what she said. I cant rememeber if she said taking a little bit of estrogen would be good and help with lowering risk of cancer and heart attacks. Or taking estrogen and progesterone together. Thats where i get confused. I do have an appt with her late tonight but i wanted to get a 2nd opinion since im on here. Help please???

        • Hi Dana…it can be confusing. Your MD may tell you that you don’t need progesterone b/c you’ve had a hysterectomy. I recommend it anyway b/c it has so many benefits beyond uterine protection. Topical estrogen is safest and will help lower the risk of cardiovascular disease and osteoporosis. The ONLY hormone that has been associated with cancer is SYNTHETIC PROGESTIN (not the same as progesterone).

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