5-alpha-reductase inhibitor

5α-Reductase inhibitor
Drug class
Dutasteride, one of the most widely used 5α-reductase inhibitors.
Class identifiers
Synonyms	Dihydrotestosterone antagonists; Dihydrotestosterone blockers
Use	Benign prostatic hyperplasia, androgenic alopecia, hirsutism, transgender women
ATC code	G04CB
Biological target	5α-Reductase
Chemical class	Azasteroids

5α-Reductase inhibitors (5-ARIs) are a class of drugs with antiandrogen effects, used primarily in the treatment of benign prostatic hyperplasia (BPH) (enlarged prostate) and androgenic alopecia (pattern hair loss). They are also used less commonly to treat hirsutism (excessive hair growth) in women.

These agents inhibit the enzyme 5α-reductase, which is involved in the metabolic transformations of a variety of endogenous steroids. 5α-reductase inhibition is most known for preventing conversion of testosterone, the major androgen sex hormone, to the more potent dihydrotestosterone (DHT), in androgen-associated disorders.

5-ARIs are clinically used in the treatment of conditions that are exacerbated by DHT:

They have also been explored in the treatment and prevention of prostate cancer. While the 5-ARI finasteride reduces the cancer risk by about a third, it also increases the fraction of aggressive forms of prostate cancer. Overall, there does not seem to be a survival benefit for prostate cancer patients under finasteride.

5-ARIs can be used in the treatment of hirsutism in women.

5-ARIs are also sometimes employed as supplementary antiandrogens in hormone replacement therapy for trans women.

In general, adverse drug reactions (ADRs) experienced with 5-ARIs are dose-dependent. Common ADRs include impotence, decreased libido, decreased ejaculate volume. Rare ADRs include breast tenderness and enlargement (gynecomastia), and allergic reaction. Other symptoms such as depression, and anxiety have been claimed with the use of 5-ARIs such as finasteride, however no significant difference in depression scores and loss of libido, compared to unaffected individuals, has been confirmed.