What Are the Dangers of Finasteride With Testosterone?

Mid adult man holding his baby
Use of finasteride in women can cause serious birth defects in male babies. (Image: Purestock/Purestock/Getty Images)

While prescription medications can have some unpleasant side effects, most diminish as your body adjusts to the drug. In other cases, side effects may persist or be worrisome enough that you should talk to your health care provider. Finasteride, a medication commonly used to treat enlarged prostate or male pattern baldness can cause several unwanted side effects, especially when testosterone levels are affected.

Enlarged Breasts

In some cases, finasteride causes changes to breast tissue during the time a man is taking the medication. Tissue in one or both breasts can enlarge if estrogen levels increase. A condition known as gynecomastia cause large breasts in men when the glands of the breasts become enlarged. The condition can also cause breast tenderness and soreness. A report published in the New England Journal of Medicine explains that gynecomastia is frequently a side effect when there is an increased ratio of estrogen to the androgen hormone, testosterone. The condition occurs when finasteride blocks the conversion of testosterone to DHT.

Testosterone is the dominant sex hormone in males; however, taking the medication finasteride can bring on gynecomastia by increasing estrogen levels. Gynecomastia affects older men in particular as the production of testosterone falls with age. The hormone that is produced is often converted to other hormones that act much like estrogen. If the condition is drug-induced, breast size usually returns to normal after stopping the medication.

Sexual Performance

Finasteride can cause a decrease in the amount of semen a male ejaculates during sexual intercourse. However, this does not affect sperm count or an individual’s ability to have children. Other adverse side effects related to sexual dysfunction may include lack of interest in sex, loss of sex drive, impotence or an inability to have or maintain an erection. According to MayoClinic.com, although less common than some of the drug’s other side effects, these side effects can occur.

Birth Defects

The male fetuses of pregnant women who use or handle finasteride are at high risk of having birth defects, warns MayoClinic.com. Studies show clear evidence of fetal abnormalities; therefore, women who are pregnant or who may become pregnant should not come in contact with the drug. The potential risk of birth defects significantly outweighs any possible benefits. Because the drug blocks the enzyme 5-alpha reductase, which converts testosterone to the hormone DHT, the genitalia of a male fetus may not develop fully.

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