Testosterone Blockers Options for Transgender Women

Transgender women are individuals who were assigned male at birth but who have a female or feminine gender identity. Although not all transfeminine individuals have a desire to undergo a medical or surgical gender transition, many do.

Often, the first step in a medical gender transition is to begin cross-sex hormone therapy. For transgender women, this involves not just the use of estrogen or estradiol but also the use of a testosterone blocker.

Hormones and Gender Presentation

There are a number of physical differences between men and women. These differences are referred to as sexual dimorphisms. (Dimorphism refers to having two different forms.) Many of these sex-linked physical differences are caused by differences in hormones.

Certain developmental changes take place differently depending on whether testosterone or estrogen is dominant in the body.

In cisgender women, estrogens dominate the body from puberty onward. The presence of more estrogen than testosterone causes breast growth. It also makes the skin softer, and there are other more subtle changes as well.

In cisgender men, testosterone predominates. It causes changes in patterns of hair growth—including male pattern baldness and facial hair growth. It causes the shoulders to widen and Adam's apple to enlarge. It thickens the vocal cords, leading the voice to drop.

High levels of testosterone can also increase a person's sex drive or aggression.

Some of these hormone-driven differences are the goals of cross-sex hormone therapy for transgender individuals. For transgender individuals, having a body that more closely matches their gender identity can decrease their dysphoria or discomfort. Cross-sex hormone therapy can move them towards that goal.

Testosterone Blockers

Testosterone acts much more strongly than estrogen does.

When people are exposed to both hormones, the effects of testosterone will surpass the effects of estrogen—this is why medical transition for transgender men is easier than it is for transgender women.

Transgender Men and Testosterone

When transgender men (assigned female at birth) are given testosterone, they experience clear masculinizing changes. They grow facial hair, their voices deepen, and their faces may subtly reshape.

These testosterone-driven changes are generally irreversible. Once someone has facial hair, it needs to be removed by laser hair removal or electrolysis. Voice pitch can be deepened by testosterone but not raised by estrogen. The bones of the face, once shifted, can only be altered by surgery.

Transgender Women and Blockers

The fact that testosterone is more efficient at masculinizing someone than estrogen is at feminizing makes transitioning more difficult for transgender women (assigned male at birth). They can't just take estrogen to develop more feminine characteristics.

They must also reduce their natural testosterone. This can be done using either testosterone blockers or surgery. The two testosterone blockers most often used for transgender women are spironolactone (also known as "spiro") and cyproterone acetate.

Currently, cyproterone acetate is not used in the United States due to concerns about liver toxicity. However, it is widely used in Europe. Some transgender women who transition early using puberty blockers may remain on those blockers to suppress their testosterone once they start cross-sex hormone therapy.

Leuprolide acetate is also sometimes used as a testosterone blocker. There are a variety of others as well.

Spironolactone

Spironolactone is the most commonly used anti-androgen in the United States. It is not just used as a testosterone blocker for transgender women, either. Spironolactone is also used to treat high blood pressure and heart failure.

Evidence suggests that spironolactone is a very safe way to lower testosterone. However, as it is a diuretic (water pill), the use of spironolactone as a testosterone blocker may cause some transgender women to require frequent urination.

Cyproterone Acetate

Cyproterone acetate is commonly used as a testosterone blocker for transgender women in Europe. Some research suggests that it is more effective at lowering testosterone levels than spironolactone. It may also improve breast growth for transgender women.

Cyproterone acetate, however, is not used in the United States. This is because the medication is associated with an increase in liver disease, including the possibility of liver cancer.

There is also some evidence that cyproterone acetate may cause other negative health consequences by decreasing HDL cholesterol and increasing amounts of the hormone known as prolactin (the hormone responsible for breast milk production).

Histrelin

Histrelin is a gonadotropin-releasing hormone (GnRH) agonist that is sometimes used as a puberty blocker for transgender youth. It is available in a number of forms, including an implant (supprelin) that lasts for up to one year. Because histrelin/supprelin is an effective way to reduce testosterone, it is sometimes continued as part of cross-sex hormone therapy. (It can also be used to treat hormone-sensitive prostate cancers.)

Histrelin is less often used as a testosterone blocker for transgender adults who start to transition after puberty, but it is an option.

Orchiectomy

Orchiectomy, or surgical removal of the testes, is a very effective way to reduce testosterone in the body. Unlike all the testosterone-blocking medications, it is permanent. Therefore, orchiectomy is usually not indicated until a person is very stable in their gender identity. It is sometimes done as part of vaginoplasty surgery, but many transgender women have no interest in this option.

Orchiectomy can be a useful option for women who can't take testosterone blockers and/or who have reasons why they should only be treated with low doses of estrogens.

Removing the testes allows transgender women to be effectively treated with much lower doses of estrogen than they would need otherwise. This can improve the safety of treatment for transgender women where estrogen treatment would otherwise be very high risk.

Guidelines for accessing orchiectomy as a gender-affirming surgery are similar to those for accessing vaginoplasty.

A Word From Verywell

Understanding how testosterone and estrogen operate in the body is helpful in order to make decisions about cross-sex hormone therapy. Discussing these options with your doctor is a great starting point if you are a transgender woman who is interested in hormonal therapy. Your doctor should evaluate your medical history and health status, as well as discuss with you your best options for proceeding.

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