Finasteride

Finasteride is the hair-loss drug that goes after the root cause rather than the symptom. It is a 5-alpha-reductase inhibitor: it blocks the enzyme that converts testosterone into DHT, the androgen responsible for the follicle miniaturisation of androgenetic alopecia.¹

A clue from genetics

The drug’s logic came from a striking natural experiment. Researchers studying people born with an inherited 5-alpha-reductase deficiency — who therefore make very little DHT — noticed that these individuals never developed male-pattern baldness (and had small prostates). If too much DHT causes the problem, blocking its production might prevent it. That insight pointed the way to a drug that does exactly that.¹

Two doses, two jobs

Finasteride reached the market first at a 5 mg dose (brand name Proscar), approved in 1992 to shrink enlarged prostates, since DHT also drives prostate growth. A much smaller 1 mg dose (brand name Propecia) was then approved in 1997 specifically for male-pattern hair loss — the same molecule, repackaged for the scalp.²

Caveats

It treats the cause, but only while taken, and it carries a well-documented set of possible sexual side effects that mean it is not for everyone. It is also approved for men; it is not used the same way in women, particularly during pregnancy.¹ Where minoxidil ignores the hormones and just pushes growth, finasteride turns the hormonal tap down — and the two are often used together.

See also

• Minoxidil, the other main drug
• Androgenetic alopecia
• Alopecia

References

1. “Finasteride.” In: StatPearls [Internet]. StatPearls Publishing (NCBI Bookshelf NBK513329). ↩ ↩² ↩³

2. PROPECIA (finasteride) tablets — U.S. FDA prescribing information. accessdata.fda.gov. ↩