The most common side effect is sexual dysfunction, which includes decrease in sexual desire, decreased semen volume and difficulty in achieving/maintaining an erection. A review of nine studies reported a 1.5% increase in sexual dysfunction in men taking finasteride, with the risk increasing with age. The sexual side effects usually resolve after stopping finasteride.
Rarely, some men experience breast tenderness/enlargement and sexual side effects that continued after stopping the medication.
In view of the different genetic makeup of individuals, not everyone taking finasteride would experience all the side effects. They are made known to you so you can make a better-informed decision.