Hormone Blockers

Hormone blockers are used for transgender adults to reduce the effect of the hormone produced by their body. For individuals transitioning from female to male the main hormone produced by the body is estrogen; for those transitioning from male to female the main hormone produced is testosterone. Transitioning is then trying to rise levels of one hormone to gain the characteristics that hormone has and limit the effects of the other hormone.

Male to Female Transitioning

Those transitioning from male to female naturally produce testosterone. Testosterone affects bone mass, fat distribution, muscle mass, sex drive, and production of sperm. Those looking to transition would like to limit the effect testosterone has on their body and introduce estrogen. The introduction of estrogen will lower muscle mass and production of sperm, reduce sperm count, change one’s sex drive, and alter fat distribution. Taking estrogen may help if one is looking for top surgery, explained father in our top surgery page. However, the body is then in a ‘fight’ between the effects of testosterone being produced in the body and the estrogen being added. To help the transitioning process some choose to take hormone ‘blockers’ to reduce the effects of testosterone and allow for estrogen to be the majority hormone found in the body.

To help aid estrogen and limit the effects of testosterone, antiandrogens are used. Androgens are male sex hormones and antiandrogens limit those hormones, the main one being testosterone. Of the antiandrogens, Spironolactone is the most commonly use in the US. Spironolactone is a potassium sparing diuretic. This type of diuretic pulls water from the body through urinating but prevents too much potassium to be lost as well, this can cause a build up of potassium in the body. Potassium affects the way your heart muscles work, too much potassium can cause a heart attack or arrythmia. Development of Hyperkalemia, high potassium levels, are rare when precautions are used, such as monitorization of its effects in the blood stream. In high doses Spironolactone acts as an antiandrogen receptor and directly suppresses the effect on testosterone synthesis. In non-transgender women doses of 200mg to 400mg per day have been used without reports of negative side effects.

Another way to block androgens is through inhibiting 5-alpha reductase. 5-alpha reductase converts testosterone into dihydrotestosterone (DHT); DHT is an androgen that is much more potent that testosterone. Inhibiting 5-alpha reductase may cause more dramatic feminizing effects, however inhibiting this enzyme does not affect the production or action of testosterone, meaning the antiandrogen effects is less than if a full blockade is used. 5-aphla reductase inhibitors are a good option for those who care unable to tolerate the use of spironolactone, or those seeking partial feminization.     

Antiandrogens do not need to be used exclusively with estrogen for short term use. Antiandrogens being used alone reduce masculinization for those first exploring reducing testosterone levels, or those who have been advised against estrogen therapy. Without the replacement of estrogen some may have symptoms of hot flashes and low moos or energy. Long term blockade without hormone replacement resulted in bone loss. Taking only antiandrogens is not a long-term solution and should be used for trials. if the outcome is unwanted, stopping the antiandrogens will allow production of testosterone as normal.

The most common class of estrogen that is used for feminizing therapy is 17-beta estradiol. 17-beta estradiol is biologically identical to the estrogen found in ovaries and is delivered via transdermal patch, oral tablet, or injection. Injection use is most common for transgender care and few outcome studies existed due to the limited use outside of transgender care. Injection versions of compounded estradiol valerate or cypionate are also used as they are more cost effective. Only take prescribed medication and prescribed dosages to stay safe, it is also important to monitor the impact these medications have on the body.    

Female to Male Transitioning

Those looking to transition to male will most likely go through masculinizing hormone therapy where the development of male secondary sex characteristics develops. General effects would include increased muscle mass, change in voice, growth of facial hair, a change in sweat and odor, a redistribution of fat, possible male pattern baldness, increased libido, clitoral growth, vaginal dryness, and cessation of menses.

All testosterone used in the U.S. are bioidentical, or chemically equivalent to naturally occurring testosterone. Testosterone is available by injection and topical preparations for those with low androgen levels. Because they are prepared for those with low, but not no testosterone higher doses may be needed for transgender care. The prior use of synthetic testosterone used by body builders have raised concern for negative hepatic effects testosterone my have on transgender men. Hepatic symptoms may include: the yellowing of skin and eyes (jaundice), abdominal pain and swelling, swelling in the legs and ankles, itchy skin, dark urine color, pale stool color, chronic fatigue, nausea or vomiting, loss of appetite, and the tendency to bruise easily. If any of these symptoms occur, please advise the care team and provider.    

Because estradiol, one of three estrogen hormones produced, varies over the menstrual cycle there is lots of overlap with natural male levels of estradiol. Estradiol plays a role in pelvic pain, persistent menses, or mood symptoms; however, it’s unclear if estrogen blockers will help manage these symptoms. If estrogen levels rise with the introduction of increased testosterone providers may prescribe estrogen blockers to help achieve hormonal balance. Though, as estrogen varies through the menstrual cycle there may not be a need for these blockers. It is always important to talk with the provider and stick with the prescribed regimen.

Puberty Blockers for Youth

Puberty blockers help delay puberty in transgender youth and are considered safe for use. As children develop differently there is not set age, though best outcomes occur when starting puberty blockers in early stages of puberty to limit the development of unwanted sex characteristics. These effects are not permanent and can be reversed by simply stopping treatment. The body will again produce sex hormones and puberty will continue as normal. Puberty blockers are meant to give more time for discovery of gender identity. Although use of puberty blockers is considered safe, they aren’t without long-term side effects; side effects may include: Lower bone density, delayed growth plate closure, and less development of genital tissue (this may limit options for gender confirmation surgery). Short term side effects include headache, fatigue, insomnia, muscle aches, changes in weight, Changes in mood, changes in breast tissue, and spotting or irregular periods (if blockers have not completely suppressed menstruating).    


Deutsch, M. B., MD, MPH. (2016, June 17). Overview of feminizing hormone therapy. Retrieved February 28, 2021, from https://transcare.ucsf.edu/guidelines/feminizing-hormone-therapy

Deutsch, M. B., MD, MPH. (2016, June 17). Overview of masculinizing hormone therapy. Retrieved February 28, 2021, from https://transcare.ucsf.edu/guidelines/masculinizing-therapy

O. (2021). Puberty blockers. Retrieved February 28, 2021, from https://www.stlouischildrens.org/conditions-treatments/transgender-center/puberty-blockers#:~:text=Puberty%20blockers%2C%20also%20called%20hormone,whether%20or%20how%20to%20transition.

GP, G. (2020, November 26). Hormone blockers for trans adults [Web log post]. Retrieved February 28, 2021, from https://www.gendergp.com/hormone-blockers-for-trans-adults/

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