Testosterone blockers, also known as anti-androgen drugs, are commonly prescribed to transgender women to block the effects of testosterone, the primary male sex hormone. By doing so, the drug can reduce some of the characteristic male traits (like facial hair and male-pattern baldness).
Testosterone blockers are taken alongside estrogen, the primary female sex hormone. In addition to promoting characteristic female traits (like breasts and pelvic bone structure), estrogen also indirectly reduces testosterone levels in the bloodstream. Testosterone
The article explains how testosterone blockers work and what drug options are available to transfeminine individuals. It also explains how orchiectomy , or the surgical removal of the testes (testicles), can eliminate the need for testosterone blockers.
Verywell Health acknowledges that sex and gender are related concepts, but they are not the same.
Research studies sometimes don't use the terminology in this way. Terms that describe gender (“woman,” “man”) may be used when terms for sex (“female,” “male”) are more appropriate. To reflect our sources accurately, this article uses terms like "female," "male," "woman," and "man" as the sources use them.
All people produce estrogen and testosterone, albeit at different levels. During puberty, different developmental changes take place depending on whether testosterone or estrogen is the dominant hormone.
In people assigned female at birth, estrogen is the hormone that dominates from puberty onward. Produced mainly by the ovaries, estrogen triggers physiologic changes that cause breasts to enlarge and the bone structure to change (such as the development of a wider pelvis).
Testosterone is also produced in smaller amounts in the ovaries as well as the adrenal glands. It plays an important role in bone health, vaginal lubrication, and libido (sex drive).
In people assigned male at birth, testosterone is the hormone that dominates from puberty onward. Produced mainly in the testes, testosterone helps spur secondary male characteristics like facial hair, an enlarged voice box (Adam's apple), and increased muscle and bone mass.
Estrogen is also produced in smaller amounts in the testes. It plays an important role in the development of sperm as well as the ability to achieve an erection (hardened penis).
Often, the first step in a medical gender transition is to begin hormone therapy, also known as gender-affirming hormone therapy.
For transgender women, this involves not only the use of estrogen (in the form of estradiol) but also the use of a testosterone blocker. This is because testosterone acts much more strongly than estrogen does.
When people are exposed to both hormones, the effects of testosterone will almost invariably surpass the effects of estrogen. This can make the process of feminization more challenging for transfeminine people.
In short, they can't just take estrogen to develop more feminine characteristics. They must also reduce their natural testosterone production or block the effects of testosterone. This is where testosterone blockers come in.
There are several drugs commonly used as a testosterone blockers in transgender women.
Aldactone (spironolactone) is the most commonly used anti-androgen in the United States. It is a type of steroid that not only works as a testosterone blocker but is also used as a diuretic ("water pill") to treat high blood pressure and heart failure.
Aldactone blocks the effects of the hormone aldosterone (which regulates fluid levels) while reducing testosterone levels in the body. It is this latter effect that makes Aldactone effective in treating symptoms like acne and hirsutism (excessive facial hair) in women with polycystic ovary syndrome (PCOS).
As a testosterone blocker, Aldactone is taken by mouth as a tablet in doses of between 50 and 300 milligrams (mg) per day. Side effects include frequent urination, dry skin, and dizziness. People with kidney problems may not be able to use Aldactone.
Finasteride is a drug widely used to treat male-pattern hair loss (under the brand name Propecia) and enlarged prostate (under the brand name Proscar).
Finasteride belongs to a class of drugs called 5-alpha reductase inhibitors that block the conversion of testosterone into the more bioactive form of testosterone called dihydrotestosterone (DHT).
In transgender women, finasteride is taken by mouth as a tablet or capsule. It is more commonly prescribed as a 1-mg daily dose (the same dose as Propecia).
Finasteride can be prescribed at a 5-mg daily dose (the same as Proscar) but may increase the risk of side effects, including low libido and swelling of the hands and feet.
In transfeminine individuals, finasteride is generally considered an alternative to Aldactone.
Avodart (dutasteride) is a 5-alpha reductase inhibitor also used to treat enlarged prostate and male-pattern baldness. As a testosterone blocker, Avodart may offer more dramatic feminizing effects than finasteride.
Avodart is taken by mouth as a gelcap at a daily 0.5-mg dose. Side effects are more or less the same as for finasteride.
As with finasteride, Avodart is a good choice for people who cannot tolerate or use Aldactone. Both can also be used in transgender women who have undergone orchiectomy but still have secondary male features like hair loss.
Eulexin (flutamide) is a type of anti-androgen used to treat hormone-sensitive prostate cancer. The same mechanism of action may be effective at reducing the effects of testosterone in transfeminine individuals.
Testosterone fuels the growth of certain prostate cancer cells. Eulexin works by binding to receptors on these cells that testosterone normally attaches to. By doing so, the drug reduces the influence of testosterone and slows the progression of the disease.
Eulexin binds to testosterone receptors in other cells as well. When used for gender-affirming therapy, Eulexin can reduce the masculinizing effects of testosterone in transgender women.
Eulexin is taken by mouth in doses between 50 and 75 mg daily. Side effects include dizziness, nausea, vomiting, diarrhea, loss of appetite, and a greenish-blue urine color. People with severe liver disease should not take Eulexin.
Suppressin LA (histrelin) is sometimes used as a puberty blocker for transgender youth. The drug histrelin is commonly used to treat hormone-sensitive prostate cancers and benign uterine fibroids.
Histrelin is a gonadotropin-releasing hormone (GnRH) agonist that blocks the release of a hormone called GnRH that directs the production of testosterone. Without ample GnRH, testosterone levels in transgender youth will drop, preventing the development of certain secondary male sex characteristics.
Supprelin LA is available as a 12-month subcutaneous implant. The implant is a narrow 1-1/2" tube that is inserted beneath the skin of the upper arm. Common side effects include localized pain, bruising, and headaches.
Supprelin LA (or any other form of histrelin) is not commonly used as a testosterone blocker in transgender adults.
Cyprostat (cyproterone acetate) is available as a testosterone blocker for transgender women in Europe. Some research suggests that it may be more effective at lowering testosterone levels than spironolactone. Even so, it is not approved for use in the United States due to concerns about liver toxicity and liver cancer.
Orchiectomy, or the surgical removal of the testes, is an effective way to reduce testosterone in transgender women. Unlike anti-androgen drugs, its effects are permanent.
Orchiectomy can often eliminate the need for testosterone blockers, although some transfeminine individuals may need to use drugs like finasteride to combat ongoing concerns like male-pattern hair loss.
Transgender women who undergo orchiectomy may also be able to take lower doses of estrogen. This reduces the risk of long-term side effects like high cholesterol, heart problems, and blood clots.
Orchiectomy is usually not used until a person is very stable in their gender identity. Even so, orchiectomy may be an early option for people who cannot take testosterone blockers for any reason (including a drug allergy or having a kidney or liver disease).
Orchiectomy is sometimes done as part of vaginoplasty surgery (the surgical construction of a vagina), although many transgender women have no interest in pursuing vaginoplasty.
Testosterone blockers, also known as anti-androgen drugs, are used to block the masculinizing effects of testosterone in transgender women. Aldactone (spironolactone) is most commonly used, but other drugs like Propecia (finasteride), Avodart (dutasteride), and Eulexin (flutamide) may also be prescribed.
For transgender youth, a subcutaneous implant called Supprelin LA (histrelin) can help prevent the development of certain secondary male characteristics during puberty.
Orchiectomy (the surgical removal of the testicles) is a permanent solution that may eliminate the need for testosterone blockers. It may also reduce how much estrogen you need to take as part of gender-affirming therapy.
Understanding how testosterone and estrogen operate in the body is helpful in order to make decisions about gender-affirming hormone therapy.
Discussing these options with your healthcare provider is a great starting point if you are a transgender woman who is interested in hormonal therapy. Your healthcare provider should evaluate your medical history and health status, as well as discuss with you your best options for proceeding.
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By Elizabeth Boskey, PhD Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.
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