Finasteride, brand name Propecia, is a medication which is often used to prevent balding, particularly the variety known as male-pattern baldness. This loss of hair is linked with the conversion of testosterone to another chemical, known as DHT. Finasteride prevents this conversion, thus blocking the signal that causes the loss of hair. Although finasteride is generally designed for adult male use, it can be used by some women, though with the risk of several side effects.
Perhaps the most serious side effect that occurs with finasteride use is serious birth defects that can occur in pregnant women. Specifically, finasteride results in defects in the sex organs of male fetuses. Because of the severity of this side effect, finasteride is not recommended for pregnant women or those who could become pregnant in the future, notes the Propecia website. The risk of this side effect is so great that premenopausal women are advised to not handle or come into contact with broken tablets of finasteride because it is not known for how long the medication stays in the body. According to the Propecia website, studies have demonstrated the safety of finasteride in women going through menopause; in these cases, there is no risk of a birth defect because of the permanent infertility of the patient. As a result, only women who have experienced menopause should take finasteride.
There are a number of side effects which are due to the effects that finasteride has on the hormonal balance in the body. These include an increase in breast size and breast tenderness, as well as decreased libido, RxList notes. This is because finasteride prevents the way that the body responds to and reacts with different hormones. One of the effects that minor alterations in testosterone can cause is an increase in estrogen production, which can cause these hormonal side effects.
Patients on finasteride have reported hypersensitivity reactions, more commonly known as allergies, as a result of using this medication, Drugs.com states. In general, a mild allergy to finasteride will result in a rash which may be itchy or cause hives. More serious allergic reactions cause swelling of parts of the body, including the face, lips, tongue and fingers.