Erectile dysfunction after taking Finasteride orally is a side effect of the drug. Finasteride is clinically used in the treatment of prostate hyperplasia, belongs to the 5α-reductase inhibitor, the mechanism of action is the male testosterone in the process of conversion to dihydrotestosterone, inhibit its conversion and thus reduce the function of the active testosterone to achieve the purpose of inhibiting prostate hyperplasia. However, inhibiting the conversion of testosterone to dihydrotestosterone effectively lowers the level of androgens, resulting in decreased sexual function or erectile dysfunction. It is recommended to use Finasteride with caution in patients who are sexually active. Clinically, Finasteride is generally not used in patients younger than 60 years of age, or patients need to be informed of the possible side effects of erectile dysfunction and decreased libido before treatment.