This insightful post was written by Dr. William Reed - a member of the Coalition of Independent Hair Restoration Physicians and can also be found on our Hair Restoration Discussion Forum.
This is not an easy question to be comfortable with in view of how delicate fetal development is and how we don’t know what we don’t know until we know that we didn’t know it… That said, however, a reassuring argument based upon what seems sound reason and good data can be put forward (so that if a woman were impregnated by someone using finasteride, he and she can feel comfortable with their situation because of the data):
Regarding female exposure: A woman can, but need not be, exposed via the dust of a quartered pill of a 5mg tablet of finasteride. I quarter my 5mg tablet by biting it and am comfortable that no powder is released to create an exposure problem. If one were not comfortable with that, then they should use the 1 mg tablet. Quoting the PDR: “PROPECIA tablets [i.e. the 1mg tablet] are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets have not been broken or crushed.” I believe that to be true.
So if the woman were not exposed by powder the other way is via semen. This, too, has understandably been well studied. Again found in the PDR are the following studies: “Semen levels have been measured 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 (5 mug) that had no effect on circulating DHT levels in men.”
This data is quite reassuring, yet we don’t know what we don’t know…. That’s why I recommend stopping finasteride during pregnancy or using condoms. This recommendation is probably treating the psychological rather than the physiological, but that’s okay.
The whole situation spins off from the male fetus at weeks 12 to 15 needing the miniscule difference of androgen that he has compared to a sister fetus because it is then that his genitalia become “male”. That’s where Dihydrotestosterone (DHT) comes in to exaggerate this small difference of testosterone that the male has since DHT is perhaps five times more powerful than ordinary testosterone. This amplification from DHT makes his male genitalia more a “black and white” result rather than some shade of grey. Five alpha reductase (which is blocked by finasteride)is the enzyme that creates the DHT from testosterone. Pretty amazing, even going beyond the miraculous, don’t you agree?
So in conclusion, in my best medical opinion, I wouldn’t worry about birth defects with finasteride if care is taken to prevent exposure to the female throughout her pregnancy and if care is taken to identify pregnancy in the first several weeks. Of course in today’s world I have to throw in the usual disclaimers that without talking personally to a patient I can’t take into account each person’s potentially unique circumstances and can’t offer specific medical advice to the individual, etc.
I hope you find this useful.
William Reed, M.D.