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The Women’s Health Initiative Study

Updated: Jun 17, 2021

Are you still using Prempro?

The Women's Health Initiative (WHI), sponsored by the National Heart, Lung, and Blood Institute (NHLBI), is a long-term national health study that focuses on strategies for preventing heart disease, breast and colorectal cancer, and osteoporosis in postmenopausal women. These chronic diseases are the major causes of death, disability, and frailty in older women of all races and socioeconomic backgrounds.

A major concern addressed early by the WHI was the increased risk of breast cancer found in those patients using Prempro. This prescription drug has the ingredients found in Birth Control Pills. It contains synthetic estrogen (Premarin) and a synthetic progestin (NOT PROGESTERONE).

What we have observed in our clinic is that many women who come to our clinic taking Prempro (post-menopausal), were not make aware of the risks established by the WHI study and often suffer from various health issues including excess body fat, moodiness, and less joy.

Breast Cancer and PremPro.

The problem, and our concern, is that the WHI established an increased risk of breast cancer, heart disease and stroke in those post-menopausal women who received the synthetic hormone called PremPro. Also, the women we see on PremPro often struggle with weight issues, poor sleep, moodiness, and other conditions that are often related to the Progestin in this synthetic formula.

We have, to the contrary, found many benefits of bioidentical progesterone for post-menopausal women (and peri-menopausal women). Progesterone is sometimes referred to as the miracle hormone for women. It is important to know the difference between progestin and progesterone. See Progesterone Blog.

What is in PremPro? It contains a progestin, medroxyprogesterone, and a conjugated estrogen.

In most prescriptions for birth control, you find a combination of progestins of various types, norethindrone acetate, norgestimate and ethinyl estradiol. Studies have shown varying risks of breast cancer depending on the form of progestin.

Note: “The estrogen-replacement drug Premarin, prescribed to menopausal women, is made from horse urine; in fact, the drug's name is short for PREgnant MARes' urINe. About 750,000 mares are impregnated each year for the sole purpose of collecting their estrogen-rich urine.” Animal rights group object to the treatment of horses that are the donors. See e.g., for more information.

A national crisis of fear occurred after publication of these results when it was announced that hormone replacement caused an increased risk of breast cancer, heart disease and stroke. After the study was completed, however, it was concluded that it was the PROGESTIN that was the cause.

The group of women in the WHI study that received estrogen alone, had less breast cancer, heart disease and stroke by 20% over the control group. The hysterectomy group did not take the progestin combination. Why? By conventional wisdom (?), they did not need Progestin as they were without a uterus. Therefore, they were not at risk for uterine cancer.

To this day, many conventionally trained physicians do not know the difference between Progestin and Progesterone. The latter has shown many benefits in women including studies showing a DECREASED risk of breast cancer, better sleep, regular periods, protection against uterine cancer, reduction of moodiness and PMS, and cessation of headaches and even migraines that may be caused by progesterone deficiency.

So, what do we glean from the WHI and other studies - do not use PremPro! Yet the product is still on the market with a warning on the package that it may increase the risk of breast cancer, heart disease or stroke.

Decrease risk of breast cancer.

In contrast to studies with progestin, a Danish study, using natural progesterone and estradiol, concluded there was a decrease in the risk of breast cancer, heart disease and stroke. There have been innumerable studies showing the benefits of natural estrogen and progesterone.

However, likely due to the power of pharmaceutical companies, PremPro continues to be marketed to post-menopausal women and their physicians.

We advocate that woman on PremPro should do the research and consider stopping this particular drug. We advocate the bioidentical hormone and functional approach to medicine that focuses on disease prevention rather than an approach that may increase the risks of diseases.

The WHI. As noted on their website:

  • The WHI is one of the largest women's health projects ever launched in the United States, having enrolled more than 161,000 women at 40 clinical centers.

  • The WHI randomized controlled clinical trial enrolled more than 68,000 postmenopausal women between the ages of 50 and 79.

  • The WHI observational study tracked the medical histories and health habits of more than 93,000 women, providing information to complement the clinical trial.

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