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What We (Don’t) Know About Estrogens

In my Trans-Health articles over the last year I have explored testosterone a few times. Now let’s try estrogens.

I won’t bore you with the details of basic physiology, organic chemistry and biochemistry. If you would like to be bored by those topics, I suggest reading the sections in my article Androgens: Under the Hood that cover these subjects. I’ll wait until you finish… and wake up.

We seem to know quite a bit more about androgens than we do about estrogens. Chemically, the classes of molecules are quite similar; the difference is significant enough, though, that a different receptor is required for estrogen to do its thang. There are actually two distinct estrogen receptors; the second was discovered within the last few years and seems to have been greeted in the research community with the same enthusiasm expressed by fans of N’Sync when the boys roll up on the tour bus. (Not that research biochemists are running around screaming, mind you, though that would be pretty hysterical….)

ER-ß (Estrogen Receptor Alpha) is found in greater numbers in the kidneys, pituitary gland and adrenal gland and has been implicated as a possible contributor to breast cancer; ER-ß (“Estrogen Receptor Beta”) is found in larger numbers in the brain and lungs. Both receptors are found in the reprouctive systems (testis, ovaries, uterus) and in breast tissue.

Estradiol, Estrone and Estriol

Estrogens are a class of molecules, much like steroids, androgens and progestins. The three molecules shown in Figures 1, 2 and 3 are the estrogens produced naturally in our bodies. There are several metabolic pathways to the creation of these estrogens, including, interestingly enough, from androgens via enzymatic conversions. They are also produced in the adrenal glands, and in the ovaries in bodies that have them.


Figure 1: Estradiol


Figure 2: Estrone


Figure 2: Estriol

The various estrogens have different avidities and affinities for the estrogen receptors. Compared to the other two, estradiol produces the most dramatic effects in the body. This is why trans women who have chosen to use hormones often use injectable versions of the hormone. The most commonly used injectable estradiol in North America is estradiol valerate.

For ease of use, the majority of trans women choose an oral version of estrogens. By far the most popular is Premarin, more generically known as conjugated estrogens. Premarin is a mixture of several different kinds of naturally occurring estrogens, some of which are not produced by the human body. (Premarin is extracted from horse urine: the story is that the brand name of the drug is shortened from the descriptive phrase “PREgnant MARe urINe,” though I cannot vouch for the veracity of that story.) I am not one of the people who thinks that Premarin is bad for you simply because it contains estrogens that the human body does not produce. I would be more concerned about using Premarin simply because it is taken orally.

Which brings me to a relevant point about taking estrogens: Estrogens have long been tied to problems with circulation and blood clots. Studies have shown that estrogen encourages the production of blood clotting factors in the liver. THIS IS IMPORTANT. If you are a woman, trans or non-trans, taking estrogen replacement, please pay attention to the symptoms of blood clotting that your physician should have warned you about when s/he prescribed them to you. Blood clots can be very dangerous, even fatal.

What does this have to do with oral drugs? Drugs that are consumed orally undergo an initial pass through the liver. As I mentioned above, the liver is the place in which the clotting factors in question are produced. Injectable preparations do not pass through the liver in the same way, and therefore they do not have the same degree of risk for clotting.

(My argumentative Type A readers will note that I did not state that injectable estrogens carry zero risk of side effects related to clotting, only that they likely do not carry the same degree of risk as oral preparations.)

How much do I take?

If you have been reading my articles for a while, you should know better than to ask me this question. Shame on you! I am not going to tell you how much to take. Only a licensed and experienced physician should make those recommendations. The most important thing to keep in mind is that supraphysiological levels of estrogen have been linked to health problems in the population that has been most thoroughly studied— menopausal and post-menopausal chromosomally XX women. I would not recommend increasing your dosage just because you can.

The two most common hormone replacement therapies for trans women in North America are injectable estradiol valerate and the oral Premarin. Therapeutic doses range from 2.5mg-10mg/day of Premarin, and 10-40mg/fortnight (two week) of estradiol valerate. Doses can be reduced significantly if the testicles are removed in surgery, either orchidectomy or GRS.

Personally, I was prescribed 10mg (1mL) of estradiol valerate, to be injected once every two weeks. I have been using it for almost 18 months and am 11 months post-orchidectomy. I am happy with the changes I have experienced on that dosage. However, one change I did make was to inject 5mg (1/2mL) once a week instead of 10mg every two weeks. I was experiencing mood swings at the end of each two week period. Switching my injections to weekly injections have cleared up that problem and now I am back to my constantly (some would say “annoyingly”) chipper self. Ask Your Doctor or Pharmacist.

There has been much more research done on hormone replacement for trans women than on hormone replacement for trans men. As such, there is a wealth of information available online and in print. Not all of it is good. Don’t take anybody’s word (including mine or your physician or endocrinologist) for anything. I have heard stupid and inaccurate statements regarding estrogen replacement therapy from a GP physician and even from an endocrinologist, both of whom had extensive experience with trans patients. If I had not done my own research, I would not have known any better.

Stay safe! And stay tuned for more technical and practical articles about hormone therapies for trans folk.


Kuiper GG, Enmark E, Pelto-Huikko M, Nilsson S, Gustafsson JA. “Cloning of a novel receptor expressed in rat prostate and ovary.” Proc Natl Acad Sci U S A 1996 Jun 11;93(12):5925-30

Kuiper GG, Carlsson B, Grandien K, Enmark E, Haggblad J, Nilsson S, Gustafsson JA. “Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta.” Endocrinology 1997 Mar;138(3):863-70

Kuiper GG, Gustafsson JA. “The novel estrogen receptor-beta subtype: potential role in the cell- and promoter-specific actions of estrogens and anti-estrogens.” FEBS Lett 1997 Jun 23;410(1):87-90

Lawson JS, Field AS, Tran DD, Houssami N. “Hormone replacement therapy use dramatically increases breast oestrogen receptor expression in obese postmenopausal women.” Breast Cancer Res 2001;3(5):342-5.

Ogawa S, Taylor JA, Lubahn DB, Korach KS, Pfaff DW. “Reversal of sex roles in genetic female mice by disruption of estrogen receptor gene.” Neuroendocrinology 1996 Dec;64(6):467-70

Razandi et al., “Plasma membrane estrogen receptors signal to antiapoptosis in breast cancer,” Molecular Endocrinology, 14:1434-47, September 2000.

Rissman EF, Early AH, Taylor JA, Korach KS, Lubahn DB. “Estrogen receptors are essential for female sexual receptivity.” Endocrinology 1997 Jan;138(1):507-10

5 thoughts on “What We (Don’t) Know About Estrogens”

  1. You are a faked Transgender. “I was prescribed 10mg (1mL) of estradiol valerate, to be injected once every two weeks. I have been using it for almost 18 months” If you check your blood work Estradilo level on the 14th day before you shoot another, you will see E2 level is lower than “Male Range”. Do not give false information to other honest Transgender.You can be delusional by yourself. Besides 10mg/ml shoot is nothing. Every transgender who use shoot (Injection) knoes it and aware of their Estradilo level in Blood work.

  2. Horrible information. Highly inaccurate. You failed to even mention that on standard OESTRODIOL is taken sublingually (under the tongue, direct into blood stream). As well, Oral, Injectable, Patch, Gel, it’s all O/Estradiol! Unless it says otherwise, which I haven’t really seen any popular ones that do. Besides Premarin(gross/promotes animal cruelty) & ethinyloestradiol (not recommended by most). Maybe it’s cause you’re not one of us, but either way you should either get your facts straight or not right the article at all.

  3. I remember in 2002 when Premarin was popular with trans girls…. Now the in thing is sublingual entrance, and NO ONE does Premarin. Funny.

    Give it a year, I bet e2v injections will be the next cool thing.

  4. I find this article refreshing. It was published quite a long time ago, but the prevailing wisdom is what is impressive. You should research your health options from all over, and not just take one person’s word as law.

    Sad to see so many negative comments attacking the writer as a fake Trans person. The article is meant to add information to people searching, not to discredit other people’s experiences.


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