Bioidentical Estrogen: What is it and is it safe?


Today I want to talk to you about something you probably have heard a lot about, and that’s bioidentical estrogens. You may be wondering what bioidentical estrogens are, and you may be wondering if they are really safe. Are they safer than the regular ones you get in a drug store? What is it you need to know to make that choice?

First, let’s begin with, “What is a bioidentical estrogen?” Bioidentical means it’s exactly the same chemical structure as the estrogens you make in your body – it’s identical. There are three estrogens that the body makes: estradiol, estrone, and estriol.

Estradiol is the main one produced by the ovary, so it’s there in the reproductive years. It’s the most potent and the most abundant of the estrogens. The second one is estrone, which is made in the fatty tissues of the body. If a person has a whole lot of abdominal fat, they’re fat is making a lot of the weak estrogen estrone. The third bioidentical estrogen is called estriol. Estriol is mostly a hormone of pregnancy. The placenta makes it, so if the woman is not pregnant, there is probably not much estriol in the body.

All the other estrogens that are available to you, such as Premarin or Cenestin, or the ones that are in birth control pills, are not bioidentical. The body thinks that the structure of those estrogens is so close to bioidentical estrogen that they actually work in the body. That’s why a hormone that has a chemical structure similar to a bioidentical one still has an effect on the body. It may be stronger, it may be weaker, or it may just be different. You can find bioidentical estrogens in most drug stores.

So now you may be wondering, are they safe? Are bioidentical estrogens ones you don’t have to worry about? Let’s remember that women have been worried, particularly in the last 10 years or so, about if estrogens increase their risk of breast cancer, blot clots, stroke, or cancer. To answer that question, I’ll ask you another: which weighs more, a pound of feathers or a pound of bricks? If you think about it, the feathers are a lot lighter, but if you get enough of them you’ll still get a full pound. So they’re the same if the amounts are equivalent.

If you are a person who’s considering taking estrogen and you want to know, “Should I take a bioidentical one or should I take a not bioidentical one,” here’s the answer to that. If you can take estrogen, all of those are going to work for you. If you can’t take estrogen, or you don’t know if you want estrogen, and you take them in equal amounts … they may not be the same number of milligrams because they are measured differently, but the risk will be the same. Remember one is a pound of bricks, one’s a pound of feathers. But if you get an equivalent amount of them, then their benefits and their potential risks are going to be the same.

If you have any other questions about bioidentical estrogens, please talk to your healthcare provider. Know the benefits and risks of estrogen before you take any medication.

Until next time,

Dr. Mache Seibel, Professor, University of Massachusetts Medical School

And Founder of My Menopause Magazine

PS: Find more information on similar topics subscribe to My Menopause Magazine, available for the iPad and iPhone in the Apple Newsstand. You can also send your questions to

Professor, University of Massachusetts Medical School

(617) 916-1880




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