5-alpha-reductase inhibitors for hirsutism

The 5-alpha-reductase inhibitors finasteride and dutasteride block the conversion of testosterone to dihydrotestosterone, the active androgen in skin. Neither drug is approved by the Australian Therapeutic Goods Administration (TGA) for the treatment of hirsutism.

Finasteride has similar effect to other antiandrogens, but it is more costly. It must be combined with a highly effective method of contraception, unless there is no risk of conception (eg the individual has had a hysterectomy or tubal ligation, is postmenopausal, or only has same-sex partners). Limited data on adverse effects of finasteride from small studies suggest they are not common. A typical regimen is:

Dutasteride should be reserved for specialist use because its efficacy has not been proven in a randomised controlled trial. It is usually only used in postmenopause; it has an extremely long half-life (4 to 5 weeks), so teratogenic risk persists for months after it is stopped.