Dutasteride measurably changes semen parameters, but the FDA label stops short of calling it a fertility risk. In the label’s 52-week study in 50 healthy volunteers, mean reductions from baseline were 23% in total sperm count, 26% in semen volume and 18% in sperm motility, adjusted against placebo. Sperm concentration and sperm morphology were unaffected. All mean values stayed within normal ranges and did not meet the study’s predefined threshold for a clinically significant change of 30%. The label’s own conclusion is that “the clinical significance of dutasteride’s effect on semen characteristics for an individual patient’s fertility is not known.” Dutasteride is contraindicated in pregnancy and in women of childbearing potential because of the risk of abnormal external genital development in a male fetus. It is FDA-approved in the United States for bph/">benign prostatic hyperplasia only; use for hair loss is off-label.
How Dutasteride Affects Male Fertility
Dutasteride suppresses DHT substantially: in men with BPH treated for 4 years, the label records a median decrease in serum DHT of 94% at 1 year. Androgens are required for spermatogenesis, which is why the effect of 5-alpha reductase inhibition on semen was studied specifically. The label does not describe a mechanism at the level of individual testicular cell types, so none is asserted here.
Clinical studies of dutasteride’s effects on semen parameters in healthy men have shown:
- Total sperm count: mean reduction of 23% from baseline at 52 weeks (FDA label). In a separate randomized, double-blind, placebo-controlled trial of 99 healthy men by Amory and colleagues, the decrease was statistically significant at 26 weeks (-28.6%) but not at 52 weeks (-24.9%)
- Sperm motility: mean reduction of 18% at 52 weeks (FDA label). The Amory trial reported a significant reduction of 6% to 12% in motility during treatment and at follow-up
- Sperm morphology: unaffected. Both the FDA label and the Amory trial state there was no effect on morphology
- Sperm concentration: unaffected (FDA label). The Amory trial recorded -3.2%, which was not significant
- Semen volume: mean reduction of 26% at 52 weeks (FDA label); -29.7% in the Amory trial, which was significant for dutasteride
- Testosterone: median increase of 19% at 1 and 2 years, 26% at 3 years and 22% at 4 years, with levels remaining within the physiologic range. Luteinizing hormone rose by a median of 12% at 6 months and 19% at 12 and 24 months. See does dutasteride increase testosterone?
These are population-level averages from a study in healthy volunteers, and the label is careful about what they do and do not mean. It notes that all mean values at all time points remained within normal ranges and did not meet the predefined criteria for a clinically significant change of 30%. It also records the tail of the distribution: 2 subjects in the dutasteride group had decreases in sperm count of greater than 90% from baseline at 52 weeks, with partial recovery at the 24-week follow-up. The label’s stated position on what this means for one man’s fertility is that it is not known.
Is Dutasteride’s Effect on Fertility Reversible?
The trial evidence points that way, with a caveat about how far it was followed. The Amory authors concluded that the decreases in semen parameters “appear reversible after discontinuation.” The follow-up data itself is less tidy than that summary suggests:
- After 24 weeks (about 6 months) off treatment, the mean total sperm count in the dutasteride group remained 23% lower than baseline (FDA label)
- At the 24-week follow-up in the Amory trial the difference from baseline was no longer statistically significant (-23.3%), while the reduction in motility was still present
- The 2 men whose sperm counts had fallen by more than 90% showed partial, not complete, recovery at 24 weeks
- No study cited in the label followed semen parameters beyond 24 weeks after stopping, so no figure for time to full recovery can be quoted
Recommendations for Men Planning to Conceive
If you plan to father children: There is no timing rule in the FDA label, and the follow-up data above does not support quoting one. What the label does establish is that dutasteride’s terminal elimination half-life is approximately 5 weeks and that serum concentrations remain detectable for up to 4 to 6 months after the last dose, and that its effect on any individual man’s fertility is not known. Take that combination to your prescribing physician and to a reproductive specialist, a urologist or a reproductive endocrinologist, and decide the timing with them rather than from a number on a web page.
- Semen analysis: A baseline analysis before starting, and a repeat after stopping, is the only way to know what happened to your own parameters rather than to a trial average. Discuss the timing with the specialist
- Sperm banking: If you are on long-term dutasteride and expect to want children, banking before starting or early in treatment is an option to raise with your clinician
- Clearance arithmetic: At a terminal half-life of approximately 5 weeks, five half-lives is about 25 weeks. The label puts it directly: serum concentrations remain detectable, above 0.1 ng/mL, for up to 4 to 6 months after treatment stops
Dutasteride in Women: Teratogenicity
⚠️ Contraindicated in Pregnancy: The FDA label contraindicates dutasteride in pregnancy and in women of childbearing potential. Dutasteride prevents the conversion of testosterone to DHT, a hormone necessary for normal development of male genitalia; in animal reproduction and developmental toxicity studies it inhibited normal development of the external genitalia in male fetuses. The label describes these abnormalities as an expected physiological consequence of 5-alpha reductase inhibition, similar to observations in male infants with genetic 5-alpha reductase deficiency. Because dutasteride is absorbed through the skin, women who are pregnant or could become pregnant must not handle the capsules. If contact is made with a leaking capsule, the label directs that the area be washed immediately with soap and water.
Dutasteride is secreted into semen, and the label quantifies it. In men taking 0.5 mg daily for 12 months, semen concentrations averaged 3.4 ng/mL, with a range of 0.4 to 14 ng/mL, which is about 11.5% of the corresponding serum concentration. Taking the highest measured value of 14 ng/mL, the label calculates that a 50-kg woman exposed to 5 mL of semen with 100% absorption would reach a concentration of roughly 0.0175 ng/mL, more than 100 times below the concentrations that produced abnormalities of male genitalia in animal studies. It also notes dutasteride is more than 96% bound to proteins in human semen, which further limits vaginal absorption. The label makes no recommendation to use condoms, and none is implied here.
Sources
- FDA. Avodart (dutasteride) prescribing information, sections 5.6, 8.1, 8.3, 12.2 and 12.3. accessdata.fda.gov
- Amory JK, Wang C, Swerdloff RS, et al. The effect of 5alpha-reductase inhibition with dutasteride and finasteride on semen parameters and serum hormones in healthy men. J Clin Endocrinol Metab. 2007;92(5):1659-65. PubMed