Anti-androgens

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Antiandrogens are a class of drugs that prevent masculinization due to androgens such as testosterone or DHT.

Overview

Class Route of administration Availability Notes
Spironolactone Steroidal antiandrogen Oral Readily available Most common antiandrogen in the US.
Cyproterone acetate Steroidal antiandrogen Oral, intramuscular injection Readily available Not approved by the FDA in the US. Common outside of the US.
Bicalutamide Nonsteroidal antiandrogen Oral Readily available Not frequently prescribed to trans people.
Enzalutamide Nonsteroidal antiandrogen Oral Available No instances of it being prescribed to trans people in medical literature.
Darolutamide Nonsteroidal antiandrogen Oral Phase III trials
Leuprorelin GnRH agonist Injection, implant Available Frequently used to block puberty.
Triptorelin GnRH agonist Injection Available
Goserelin GnRH agonist Implant Available
Finasteride 5α-reductase inhibitor Oral Readily available Often prescribed for hair loss.
Dutasteride 5α-reductase inhibitor Oral Readily available Sometimes prescribed for hair loss.
Estradiol Antigonadotropin Oral, sublingual, injection, implant, transdermal, others Readily available

Mechanism of action

Spironolactone

Spironolactone has two primary factors that contribute to its antiandrogenic activity:

  • Androgen receptor partial agonism: Spironolactone binds to the androgen receptor and causes it to express much more weakly than if an androgen such as testosterone or DHT had bound to it.
  • 17α-hydroxylase and 17,20-lyase inhibition: These two enzymes are key in the steroidogenesis of androgens (and estrogens and some glucocorticoids).

Cyptoterone acetate

Cyproterone acetate has two primary factors that contribute to its antiandrogenic activity:

  • Androgen receptor partial agonism: Cyproterone acetate binds to the androgen receptor and causes it to express much more weakly than if an androgen such as testosterone or DHT had bound to it.
  • Progestogenic activity: Cyproterone acetate acts as a progestogen, inducing negative feedback on the HPG axis. In people with testes, this results in lower testosterone levels. In people with ovaries, this results in lower estrogen levels.

Bicalutamide

Bicalutamide is a nonsteroidal androgen receptor antagonist. It binds to the androgen receptor and prevents the expression of AR-regulated genes.

Enzalutamide

Enzalutamide is a nonsteroidal androgen receptor antagonist. It binds to the androgen receptor and prevents the expression of AR-regulated genes.

Darolutamide

Darolutamide is a nonsteroidal androgen receptor antagonist. It binds to the androgen receptor and prevents the expression of AR-regulated genes.

Leuprorelin

Leuprorelin is a GnRH agonist. It induces strong positive feedback on the HPG axis, which causes an increase in LH, FSH, testosterone (in males), and estrogen (in females) levels. After some time, the body downregulates the GnRH receptor, causing LH, FSH, endogenous testosterone (in males), and endogenous estrogen (in females) levels to drop.

Triptorelin

Triptorelin is a GnRH agonist. See #Leuprorelin for mechanism of action.

Goserelin

Goserelin is a GnRH agonist. See #Leuprorelin for mechanism of action.

Finasteride

Finasteride is a 5α-reductase inhibitor. 5α-reductase is an enzyme involved in the biosynthesis of DHT from testosterone. DHT is a more potent androgen receptor agonist than testosterone.

Note that finasteride does not prevent testosterone from binding to the androgen receptor, so finasteride alone is insufficient to prevent masculinization.

Dutasteride

Dutasteride is a 5α-reductase inhibitor. See #Finasteride for mechanism of action.

Note that dutasteride does not prevent testosterone from binding to the androgen receptor, so dutasteride alone is insufficient to prevent masculinization.

Estradiol

Estradiol is a antigonadotropin. It induces negative feedback on the HPG axis, which causes the body to produce less testosterone (in males) or estrogen (in females).