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Estrogen Side Effects:  What You Need to Know

Information on the internet about estrogen and estrogen side effects is full of confusion and misinformation. I hope that I can give you some new information that will help you learn what you need to know.  

Which estrogen are you talking about?

You can't just speak about estrogen as if it is one substance.  First you must clarify which estrogen you are talking about.

One use of the word “estrogen” is to refer to a group of female hormones produced by your body.  The three major estrogens are estradiol, estriol and estrone.  These are the human estrogens.  The drawing below is a molecule of human estrogen.

Then there are the conjugated estrogens, which are the estrogens that have been used in traditional hormone replacement therapy.  Most of these estrogens are formulated from pregnant mare's urine.

Some brand names are Premarin, Prempro (contains progestin), Premphase (also contains progestin)

The Free Dictionary defines conjugated estrogens as “a mixture of sodium salts of estrogen sulfates, chiefly those of estrone, equilin, and 17-alpha-dihydroequilin.”  Equilin and 17-alpha-dihydroequilin are both estrogens from horses.

Finally, there are the bioidentical estrogens.   The Dictionary.com site defines bioidentical: “possessing identical molecular structure especially in relation to an endogenously produced substance “    (Dictionary.com)

So first there are the hormones your body makes.  Then there are the chemically identical (bioidentical) to human hormones that are made in a lab.  And there are the hormones (conjugated) that are not chemically identical and are made in a lab.  Horse estrogen is not chemically identical to human estrogen.  

So.  Both types of hormones are made in a lab.  Both types of hormones may use a plant source of estrogen in their product.  The DIFFERENCE is this:  the chemical structure.  That is all you need to concern yourself with.  Not what it's made of, or from, or where.  What is the chemical structure?  Is it identical to your human hormone molecular structure, or not?  Simple, really.  Just ignore all the hype and philosophizing going on around it.

Speaking of hype and philosophizing, I notice when I review other websites for estrogen side effects, that even though many of the sites suggest that bioidentical hormones are riskier because they have not been scientifically studied the way the conjugated estrogens have, they then go ahead and lump the two together when talking about estrogen side effects and risks.  

The author will say something like, don't use this type of hormone because we don't know how it acts in the body, but we're sure that it must at least have the same side effects and risks of the the hormone type we HAVE studied.  Sorry, that doesn't make much sense.

Harvard Health Publications has a nice chart that gives you the brand name and tells you whether or not it's bioidentical.

Common Estrogen Side Effects for Estradiol, a Bioidentical Estrogen (from drugs.com)

“Breast pain or tenderness; headache; hair loss; mild nausea or vomiting; spotting or breakthrough bleeding; stomach cramps or bloating.

Seek medical attention right away if any of these SEVERE side effects occur when using Estradiol: 

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); back pain;breast discharge or lump in the breast; calf or leg pain or swelling; chest pain; coughing up blood; dark urine; depression; dizziness; fainting; fever; memory problems; mental or mood changes; muscle pain; one-sided weakness; painful or difficult urination; persistent or severe breast pain or tenderness; persistent or severe headache, nausea, or vomiting; severe stomach pain or swelling; slurred speech; sudden shortness of breath; sunburn-like rash; swelling of hands, legs, or feet; unusual vaginal bleeding, discharge, itching, or odor; vision changes; vomiting; weakness or numbness of an arm or leg; yellowing of the skin or eyes.”

Here are estrogen side effects for a conjugated estrogen, Premarin

According to the Physician's Drug Handbook (5th Edition), Premarin, a conjugated estrogen, has the following potential side effects:  headache, dizziness, chorea, depression, libido changes, lethargy, thrombophlebitis, thromboembolism, hypertension, edema, increased risk of stroke, pulmonary embolism, myocardial infarction, melasma, urticaria, acne, sebarrhea, oily skin, hirsutism or hair loss, worsening of myopia or astigmatism, intolerance to contact lenses, nausea, vomiting, abdominal cramps, bloating, diarrhea, constipation, anorexia, increased appetite, weight changes, breakthrough bleeding, altered menstrual flow, dysmenorrhea, amenorrhea, cervical erosion, altered cervical secretions, enlargement of uterine fibromas, vaginal candidiasis, cholestatic jaundice, hyperglycemia, hypercalcemia, folic acid deficiency, breast changes (tenderness, enlargement, secretions), leg cramps

And here is the Drugs.com version of Estrogen Side Effects for Premarin:  Common

“Back pain; bloating; breast pain; depression; diarrhea; dizziness; flu syndrome; gas; hair loss; headache; increased cough; increased/decreased interest in sex; indigestion; infection; irregular vaginal bleeding or spotting; itching; joint pain; lightheadedness; leg cramps; muscle aches; nausea; nervousness; pain; runny nose; sinus inflammation; sleeplessness; sore throat; stomach pain; upper respiratory tract infection; vaginal inflammation; weakness; weight changes.

Seek medical attention right away if any of these SEVERE side effects occur: 

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); abnormal bleeding from the vagina; breast lumps; changes in vision or speech; chest pain; confusion; dizziness; fainting; hoarseness; mental/mood changes; one-sided weakness; pain or tenderness in the upper abdomen; pain or tenderness in the calves; severe headache; sudden shortness of breath; swelling of the hands or feet; unusual vaginal discharge/itching/odor; vomiting; weakness or numbness of an arm or leg; yellowing of the skin or eyes.”

And here are some risks that were scientifically proven using conjugated estrogens:

According to the National Institute of Health website, “The Women's Health Initiative (WHI) was a major 15-year research program to address the most common causes of death, disability and poor quality of life in postmenopausal women -- cardiovascular disease, cancer, and osteoporosis.”

“The WHI was launched in 1991 and consisted of a set of clinical trials and an observational study, which together involved 161,808 generally healthy postmenopausal women.

The clinical trials were designed to test the effects of postmenopausal hormone therapy, diet modification, and calcium and vitamin D supplements on heart disease, fractures, and breast and colorectal cancer.

The hormone trial had two studies: the estrogen-plus-progestin study of women with a uterus and the estrogen-alone study of women without a uterus. (Women with a uterus were given progestin in combination with estrogen, a practice known to prevent endometrial cancer.) In both hormone therapy studies, women were randomly assigned to either the hormone medication being studied or to placebo.”

(Women's Health Initiative, 2010)

The results of the study:

Women taking estrogen plus progestin, compared to those taking placebo:

Increased risk of heart attack, stroke, blood clots, and breast cancer.  The only benefits were fewer fractures and reduced risk of colorectal cancer.

Women taking estrogen only, compared to those taking placebo:

Increased risk of stroke and blood clots.  Reduced risk of fracture.

So we have some information about estrogen side effects from science for conjugated estrogens.  We don't have much information from science about bioidentical estrogen side effects.  Depending on which website you visit, an author may be so pro-bioidentical that they make all kinds of unsubstantiated claims.  On the other hand, an author may be so anti-bioidentical they err in the other direction.  What does it all mean?  To answer that question, we need to step back and ask bigger questions.

Does Science Have the Truth?

One of my favorite all-time quotes from a fascinating book will shed some light on our revered Science:  “In 1962 a physicist turned historian published a remarkable analysis of science.  Ostensibly it describes how scientific theories and assumptions about nature are changed by social and subjective factors rather than “objective” criteria, and how there is no progress in science, only changing perspectives.”  (Briggs & Peat, 1984, p 18).  The authors in this book are referring to Thomas Kuhn and his book, The Structure of Scientific Revolutions.

The book, Looking Glass Universe, covers the recent revolutionary theories developed by scientists in physics, chemistry, biology and neurophysiology – theories that turn our current understanding of how the universe works on its head.

Think about the time when everyone “knew” the world was flat.  When certain people started saying the world was round, do you think people listened?  Or did they call them crazy?

This may seem a long way off topic for estrogen side effects, but I am trying to give you a perspective that allows you to see the current medical conversation for what it is.  There are those that rely on scientific evidence for their Truth.  There are others open to new ideas.  And there are women who relied on word-of-mouth and historical uses and outcomes when they used herbs for healing, for thousands of years before modern medicine came along and said, you can't rely on that because there is no scientific evidence.

I hope that I have been able to answer some of your questions about estrogen side effects.  Or maybe you have more questions now than you did before.  It's your choice whether or not to use conventional HRT, or bioidentical hrt, or herbs, diet and exercise.  Only you know how functional you are or are not, and only you know how comfortable you will be with the taking the risks associated with HRT, and putting up with potential estrogen side effects.

For more about bioidentical hormone therapy, see these related pages.

Bioidentical hormone therapy

Natural estrogen replacement


Briggs, J. & Peat, F.D. (1984).  Looking Glass Universe.  Cornerstone Library.  New York: NY

Dictionary.com.  Bioidentical.  Retrieved July 4, 2011 from http://dictionary.reference.com/browse/bioidentical

Drugs.com  Side effects of estradiol.  Retrieved July 4, 2011 from http://www.drugs.com/sfx/estradiol-side-effects.html 

Free Dictionary.  Conjugated Estrogens.  Retrieved July 4, 2011 from http://medical-dictionary.thefreedictionary.com/conjugated+estrogen

Physician's Drug Handbook, 5th Edition.  Springhouse Corporation: Springhouse, PA

Women's Health Initiative (9/21/2010).  Retrieved July 3, 2011 from http://www.nhlbi.nih.gov/whi/

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