From the FDA Drug Label
8.1 Pregnancy Risk Summary Finasteride tablets are contraindicated in pregnant females and not indicated for use in females. Based on animal studies and the mechanism of action, finasteride tablets may cause abnormal development of external genitalia in a male fetus if administered to a pregnant female [see Warnings and Precautions (5.3) and Clinical Pharmacology (12. 1)]. In an embryo-fetal development study in rats, there was a dose-dependent increase in hypospadias that occurred in 3.6 to 100% of male offspring of pregnant rats administered oral finasteride during the period of major organogenesis at doses approximately 0.1 to 86 times the maximum recommended human dose (MRHD) of 5 mg/day (based on AUC at animal doses of 0. 1 to 100 mg/kg/day). Abnormal male genital development is an expected consequence when conversion of testosterone to 5α-dihydrotestosterone (DHT) is inhibited by 5α-reductase inhibitors.
Finasteride and Birth Defects:
- Finasteride may cause abnormal development of external genitalia in a male fetus if administered to a pregnant female.
- Hypospadias occurred in 3.6 to 100% of male offspring of pregnant rats administered oral finasteride.
- Abnormal male genital development is an expected consequence when conversion of testosterone to 5α-dihydrotestosterone (DHT) is inhibited by 5α-reductase inhibitors. Based on the information provided, finasteride may cause birth defects, particularly abnormal development of external genitalia in male fetuses, if taken by pregnant females 1.
From the Research
Finasteride can cause birth defects in male fetuses if pregnant women are exposed to it, which is why it carries a pregnancy category X rating. Women who are pregnant or may become pregnant should not handle crushed or broken finasteride tablets due to the risk of absorption through the skin. The primary concern is that finasteride inhibits the conversion of testosterone to dihydrotestosterone (DHT), which is essential for normal male genital development during pregnancy. Exposure during pregnancy can lead to abnormalities of the external genitalia in male fetuses, including hypospadias (abnormal positioning of the urethral opening), ambiguous genitalia, and underdeveloped genitals.
Key Considerations
- Men taking finasteride should use reliable contraception if their sexual partner could become pregnant.
- Men should not donate blood while taking finasteride and for at least one month after stopping treatment to prevent potential exposure to pregnant women through blood transfusions.
- There is no evidence that finasteride affects sperm parameters or fertility in men, so men planning to father children do not need to discontinue the medication for this reason, as supported by a study from 2.
- A case report from 2 found that maternal use of finasteride in early pregnancy was not associated with external genitalia abnormalities of a male baby, but this does not indicate safety of use.
Clinical Implications
- The use of finasteride during pregnancy may carry the risk of birth defects, especially hypospadias, as reported in a case report from 2.
- Population-based long-term neonatal outcomes are yet to be established, highlighting the need for further research on the topic.
- The mechanism of action of finasteride, inhibiting the conversion of testosterone to dihydrotestosterone, is essential for understanding its potential effects on fetal development, as discussed in a review from 3.
Recommendations
- Women who are pregnant or may become pregnant should avoid exposure to finasteride.
- Men taking finasteride should be aware of the potential risks and take necessary precautions to prevent exposure to pregnant women.
- Healthcare providers should discuss the potential risks and benefits of finasteride with patients, particularly those who may be planning to father children or have partners who are pregnant or may become pregnant, as suggested by a study from 4.