Finasteride is an anti-androgen agent used to treat benign prostatic hyperplasia and male pattern baldness. This medication works by inhibiting the 5 alpha reductase enzyme that converts the male sex hormone testosterone into its more potent form, dihydrotestosterone (DHT).
The side effects seen with this drug are therefore related to its anti-androgenic effects. Since both benign prostatic hyperplasia and male pattern baldness require long-term and continuous use of the drug, the risk of side effects is high.
One 12 month clinical trial of 5 mg finasteride versus placebo in 3000 patients showed that the side effects associated with finasteride include:
Patients taking finasteride to treat benign prostatic hyperplasia may find that symptoms such as difficulty urinating, increased urination frequency and decreased urinary flow improve after around six months of treatment. These beneficial effects, however, are reversed and symptoms worsen when the medication is discontinued.
Finasteride has also been shown to benefit men with mild to moderate hair loss. Again, the medication is only effective for as long as it is used, with the therapeutic effects being lost within 6 to 12 months after discontinuation of the therapy.
Finasteride causes defects of the sexual organs in the male fetus. Pregnant women or women who are likely to be pregnant should therefore be careful not to handle crushed finasteride tablets in order to avoid its absorption via the skin.