The Difference Between Bioidentical Progesterone and Synthetic Progestins

Let’s talk about progesterone and progestins. They are 2 very similar words, but from a hormone balance standpoint, they couldn’t be more different.

Both provide a counterbalance to estrogen that helps protect the uterus from a constant estrogen barrage. This helps reduce the likelihood of uterine cancer.

This is where the therapeutic similarities end. 

What is Progesterone?

Progesterone is the hormone that is primarily produced in the second half of your menstrual cycle. In the first 14 days of the cycle, estrogen is in charge. Estrogen’s job is to grow the cells of the uterus to prepare it for implementation of a fertilized egg. 

At day 14, presumably when ovulation occurs, progesterone production ramps up in case you become pregnant. If a fertilized egg implants itself, progesterone levels will continue to rise. If not, progesterone drops, signaling the end of the cycle, and the whole process starts over again.

But that’s not progesterone’s only job. 

Progesterone receptors are located in the blood vessels, the liver, breast tissue, the bone, and the brain. This hormone has an important influence in the functioning of all those parts of the body. 

Most of your progesterone is produced by ripened eggs. That means when your ovaries slowly wind down their function and you stop ovulating, progesterone production slows down dramatically. Your adrenals pick up a bit of the slack, but not in quantities that are enough to oppose estrogen.

Estrogen is produced by other cells in the body besides the ovaries, namely fat cells and to a small extent, by the adrenal glands, so it’s easy to see how things can get out of balance

What are Progestins?

Progestins are synthetic forms of progesterone and are found in birth control pills, IUDs and products like Prempro, Provera and Depo-Provera. They have a somewhat similar chemical structure to progesterone, but they do not have the same side effects or therapeutic benefit.

While they are useful for opposing estrogen and providing protection against uterine cancer, they do not provide the same positive health effects of progesterone (easing anxiety, bone health, help with insomnia, etc.) and are not well tolerated by some women. Side effects include: abdominal pain or cramping, bloating or swelling of ankles or feet, blood pressure increase, dizziness, headache, mood changes, nervousness, and unusual or rapid weight gain.

Why is There So Much Confusion??

The medical community and drug manufacturers have lumped progesterone into the progestin category and these words are often used interchangeably despite the differences between them. This causes huge amounts of confusion for women when it comes to managing hormone imbalances and making choices regarding therapy.

Does Progesterone Cause Cancer?

Progesterone has NEVER been implicated in causing breast cancer and in fact, has a protective effect. You can read more about that here. It is safe to use by itself. Progesterone is helpful for many women, but it’s not a magic bullet. You and your provider need to look at the whole picture of hormones and health to determine if it’s a good idea to use it or not.

Synthetic progestins HAVE been shown to increase the risk of breast cancer (Women’s Health Initiative Study 2002) and I generally recommend avoiding them if possible. This increase also extends to birth control pills and hormone-containing IUDs. If you’re on the fence or afraid to try progesterone, I can help you with that. Don’t suffer, get the real 411 from a health care professional and menopause expert. Find out more about that here:

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Dr. Anna Garrett is a menopause expert and Doctor of Pharmacy. She 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. Dr. Anna is the author of Perimenopause: The Savvy Sister’s Guide to Hormone Harmony. Order your copy at

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