Long-term use of dutasteride to treat androgenic alopecia in young men may lead to persistent abnormalities in semen parameters.

Objective: To evaluate the long-term effects of dutasteride on male fertility and determine the cutoff treatment duration that causes significant and persistent decreases in semen parameters.

Methods: This was a single-center, randomized, controlled study that evaluated 200 men (ages 28 to 39 years). Forty men were allocated to each study group, divided according to the duration of dutasteride treatment, as follows: <6 months (group 1), 6-12 months (group 2), 13-18 months (group 3), 19-24 months (group 4), and >24 months (group 5). All subjects received dutasteride 0.5 mg/day for management of androgenetic alopecia then discontinued dutasteride for 6 months.

Results: The baseline mean testosterone level in the study subjects was 4.8 ng/mL. No significant differences were found between study groups in sperm concentration, normal morphology, and vitality. Semen volume and sperm total/progressive motility were significantly reduced as the duration of dutasteride treatment increased. All study groups showed an increase in total sperm motility and semen volume after discontinuation of dutasteride. Compared with group 1, groups 2-5 showed significant decreases in semen volume and sperm total motility, with the odds ratios becoming smaller as the duration of dutasteride treatment increased. Receiver operating characteristic analysis showed the cutoff values for persistent impairment of semen volume and total sperm motility to be 17.8 and 20.3 months, respectively.

Conclusion: Long-term use of dutasteride may lead to male infertility by persistently impairing semen volume and sperm motility.