Gynaecomastia and Finasteride, The Science and Biochemistry

It seems paradoxical at first: finasteride lowers DHT, which is an androgen, so why would the breasts grow? The answer is that DHT is only one part of the hormonal balance controlling male breast tissue. The key is the testosterone–DHT–oestrogen balance Finasteride inhibits 5-alpha-reductase, the enzyme that converts testosterone into dihydrotestosterone (DHT). Finasteride → ↓ DHT But the testosterone that would otherwise have been converted to DHT remains available. Some of that testosterone can be converted by aromatase into oestradiol: Testosterone → aromatase → oestradiol Finasteride doesn't directly increase aromatase, and it doesn't usually produce a dramatic increase in oestradiol. However, the combination of less DHT's anti-oestrogenic/androgenic influence and a relative shift in the androgen–oestrogen balance can favour breast-tissue stimulation in susceptible men. Why does DHT matter to breast tissue: DHT is a particularly potent androgen. It acts through the androgen…