Finasteride: uses, dosing, side effects & brands

PROPECIA (finasteride) tablets contain finasteride as the active ingredient. Finasteride, a synthetic 4-azasteroid compound, is a specific inhibitor of steroid Type II 5α-reductase, an intracellular enzyme that converts the androgen testosterone into 5α-dihydrotestosterone (DHT).

The FDA classifies finasteride as a 5-alpha reductase inhibitor. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.

The elimination half-life of finasteride is about 5 to 6 hours in men aged 18 to 60 (mean terminal half-life; after IV dosing the label reports a mean of 4.5 hours, range 3.3 to 13.4 hours) — that is how long the body takes to clear half of a dose. This is the terminal (elimination) half-life of finasteride itself, as stated in the FDA label's Clinical Pharmacology section. Age: the label says mean terminal half-life rises to about 8 hours in men over 70, but no dosage adjustment is recommended. Kidney: in chronic renal impairment (creatinine clearance 9 to 55 mL/min) the label reports half-life, AUC, peak concentration and protein binding after a single dose were similar to healthy volunteers, with more of the metabolites leaving in the feces instead of the urine; no dosage adjustment is necessary. Liver: finasteride is extensively metabolized by CYP3A4, and this label gives no half-life data in hepatic impairment, so none is reported here. Metabolites: finasteride is not a prodrug, and its two identified metabolites have no more than 20% of finasteride's 5-alpha-reductase inhibitory activity, so there is no active metabolite that outlasts and substitutes for the parent. One important caveat: the drug's biological effect outlives the drug in the blood. The label notes the finasteride-enzyme complex turns over slowly (half-life roughly 30 days for the Type II enzyme complex and 14 days for Type I), so DHT suppression persists well after plasma finasteride has cleared. Plasma half-life is not a detection window and not dosing guidance. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run finasteride against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

We track 3 finasteride-containing products in the U.S.: Propecia, Proscar and Finasteride. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

Across the brands we track, finasteride is currently marketed as tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Yes. Our catalog lists 1 generic finasteride product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.

The FDA's Enforcement database lists 1 recall record whose product description mentions finasteride. The most recent: Finasteride NDC# 82187-1003-1 Container Description: The product packed in whit… (Feb 7, 2025). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.

The most common are sexual side effects: decreased sex drive, difficulty getting or keeping an erection, and reduced volume of ejaculate. These affect a minority of men and often improve with continued use or resolve after stopping, though some men report that sexual effects persist. Finasteride blocks conversion of testosterone to DHT, which is how it treats hair loss and enlarged prostate.

Report breast changes — lumps, pain, enlargement, or nipple discharge — because male breast cancer has been reported in men taking finasteride. Also tell your doctor about new depression or suicidal thoughts, which have been reported. Signs of a serious allergic reaction (swelling of the lips, face, or throat; trouble breathing) need emergency care.

Finasteride can cause abnormalities in the genitals of a developing male fetus. Women who are or may become pregnant must not handle crushed or broken tablets, because the drug can be absorbed through the skin. Whole tablets are coated to prevent contact during normal handling, but a broken one is a real exposure risk. Finasteride is only for men and is not prescribed to women of childbearing potential.

Yes. Finasteride lowers PSA (prostate-specific antigen) levels by about half, even if prostate cancer is present. Tell any doctor ordering a PSA test that you take finasteride so the result can be interpreted correctly — a normal-looking PSA may need to be roughly doubled to compare against untreated values. A rising PSA while on finasteride should be evaluated.

Some drop in libido or ejaculate volume is a known, generally non-dangerous effect that you can discuss with your prescriber. What is not routine: breast lumps or discharge, new or worsening depression or suicidal thoughts, and any facial or throat swelling — those need prompt medical attention. Pregnancy-handling precautions are absolute, not optional.