Anti-androgen
Quick Definition
An anti-androgen is a medication that reduces or blocks androgen activity in the body. Mechanisms include reducing androgen production, blocking the androgen receptor, and inhibiting the conversion of testosterone to DHT. The category includes 5-alpha-reductase inhibitors, androgen receptor blockers, and some other agents.
In Depth
Anti-androgens reduce or block androgen activity through several distinct mechanisms:
- Production suppression. GnRH analogs (leuprolide) reduce gonadotropin release, reducing testicular testosterone production. - Conversion inhibition. 5-alpha-reductase inhibitors (finasteride, dutasteride) reduce conversion of testosterone to DHT. - Receptor blockade. Androgen receptor antagonists (bicalutamide, flutamide, spironolactone) compete with testosterone and DHT at the receptor.
Clinical contexts:
- Male pattern hair loss. 5-alpha-reductase inhibitors (finasteride, dutasteride) are the dominant anti-androgens used. - Prostate cancer. GnRH analogs and androgen receptor antagonists are first-line. - Benign prostatic hyperplasia. 5-alpha-reductase inhibitors reduce prostate volume. - Female androgenic conditions (hirsutism, female pattern hair loss). Spironolactone is widely used. - Gender-affirming care. Multiple anti-androgens are used in feminizing hormone therapy.
Side effects shared across the class generally relate to reduced androgen activity: decreased libido, erectile dysfunction in men, breast tenderness or enlargement, mood effects in some patients, and effects on body composition.
5-alpha-reductase inhibitors are uniquely positioned in the anti-androgen category — they reduce DHT specifically without lowering testosterone, in fact they often modestly raise circulating testosterone. This profile makes them useful for hair loss without producing the libido and energy effects associated with testosterone-suppressing anti-androgens.
Anti-androgens are contraindicated in pregnancy when the fetus is genetically male, due to potential effects on male fetal development.
Related Terms
Dutasteride
Dutasteride is a dual 5-alpha reductase inhibitor that blocks both Type I and Type II isoforms of the enzyme responsible for converting testosterone into dihydrotestosterone (DHT). The FDA approved dutasteride (brand name Avodart) in 2001 for the treatment of benign prostatic hyperplasia (BPH) in adult males. By reducing DHT levels throughout the body by up to 90%, dutasteride has also been studied and used off-label for androgenetic alopecia (male pattern hair loss), though this indication has not received FDA approval. Dutasteride is available as a 0.5 mg capsule taken once daily, and compounded formulations may be prescribed by licensed providers for hair loss. Because it is more potent and has a longer half-life than finasteride, dutasteride requires careful patient selection and monitoring by a healthcare provider.
Finasteride
Finasteride is a Type II 5-alpha-reductase inhibitor FDA-approved for male pattern hair loss (1 mg, Propecia) and benign prostatic hyperplasia (5 mg, Proscar). It works by reducing dihydrotestosterone (DHT), the androgen most directly responsible for follicular miniaturization in male pattern baldness.
5-alpha-reductase Inhibitor
A 5-alpha-reductase inhibitor is a medication that blocks the conversion of testosterone to dihydrotestosterone (DHT). The class is FDA-approved for benign prostatic hyperplasia and male pattern hair loss. It includes finasteride (Type II selective) and dutasteride (Type I and Type II).
Selective Estrogen Receptor Modulator
A selective estrogen receptor modulator (SERM) is a medication that selectively activates or blocks the estrogen receptor depending on the tissue. SERMs include tamoxifen (breast cancer), raloxifene (osteoporosis), and clomiphene/enclomiphene (ovulation induction in women, secondary hypogonadism in men).