Finasteride

Key points

• Propecia is indicated for male pattern hair loss in men only. The label states it is not indicated for use in women, and efficacy in bitemporal recession has not been established.
• The most common adverse reactions, reported in 1% or more of men treated and more often than on placebo, are decreased libido, erectile dysfunction and ejaculation disorder.
• The label records sexual dysfunction that continued after treatment stopped, including erectile dysfunction, libido disorders, ejaculation disorders and orgasm disorders, together with male infertility or poor seminal quality.
• Finasteride is a competitive and specific inhibitor of Type II 5-alpha-reductase, the intracellular enzyme that converts testosterone into dihydrotestosterone.

How it works

In men with male pattern hair loss, the balding scalp contains miniaturised hair follicles and increased amounts of dihydrotestosterone, and finasteride decreases scalp and serum DHT concentrations in those men. The label is careful about how far that explanation reaches: the relative contributions of those reductions to the treatment effect have not been defined, and finasteride appears to interrupt a key factor in the development of androgenetic alopecia in men who are genetically predisposed. Finasteride is extensively metabolised in the liver, primarily via the cytochrome P450 3A4 enzyme subfamily.

Safety specific to finasteride

Sexual adverse effects, and their persistence. Decreased libido, erectile dysfunction and ejaculation disorder are the most common adverse reactions on this label, each reported in 1% or more of treated men and more often than on placebo. The label also asks physicians to inform patients that finasteride may cause these symptoms, including decreased ejaculate volume. Separately, under postmarketing experience, it records sexual dysfunction that continued after discontinuation of treatment, covering erectile dysfunction, libido disorders, ejaculation disorders and orgasm disorders, along with male infertility or poor seminal quality, for which normalisation or improvement has been reported after stopping.

Depression and suicidal ideation. The label’s postmarketing experience section lists depression, and suicidal ideation and behaviour, under nervous system and psychiatric reactions. On a medicine taken for appearance, largely by men in their twenties and thirties, this is not a footnote.

Women and pregnancy. Finasteride is not indicated for use in women. Women who are pregnant or may potentially be pregnant should not handle crushed or broken tablets, because of the possibility of absorbing finasteride and the subsequent potential risk to a male fetus. The tablets are coated and will prevent contact with the active ingredient during normal handling, provided they have not been broken or crushed.

Prostate specific antigen. Finasteride lowers serum PSA, which matters for anyone whose prostate is being monitored. The label also notes that men aged 55 and over taking a 5-alpha-reductase inhibitor were found to have an increased risk of high-grade prostate cancer.

Children. The label states finasteride is not indicated for use in paediatric patients.

When to seek urgent care

New or worsening low mood, hopelessness, or thoughts of self-harm during treatment warrant prompt medical attention rather than waiting to see whether they settle. Sexual adverse effects that persist after stopping should also be raised with a doctor, since the label records them as reported outcomes rather than as expected recovery.

Further reading

• PROPECIA- finasteride tablet, film coated
• Propecia 1 mg Film-Coated Tablets