Every now and then we see patients who are willing to start or continue finasteride (Propecia) for treatment of his hair loss, but are concerned with the possible adverse effects on the baby. Below I put the exact paragraph as stated in the medication brochure based on the research that has been done:
Semen levels have been measure in 35 men taking finasteride 1 mg/day for 6 weeks. In 60% (21 of 35) of the samples, finasteride levels were undetectable (<0.2 ng/mL). The mean finasteride level was 0.26 ng/mL and the highest level measured was 1.52 ng/mL. Using the highest semen level measured and assuming 100% absorption from a 5-mL ejaculate per day, human exposure through vaginal absorption would be up to 7.6 ng per day, which is 750 times lower than the exposure from the no-effect dose for developmental abnormalities in Rhesus monkeys and 650-fold less than the dose of finasteride (5mg) that had no effect on circulating DHT levels in men.[/bq] In conclusion, it is highly probable that Propecia will not cross into the woman’s vagina in any significant quantity.