Finasteride: what it treats, how to take it, side effects
Last updated September 3, 2026.
Finasteride is a 5-alpha reductase inhibitor - it blocks production of a male hormone that enlarges the prostate and stops hair growth. You may know it as Proscar for the prostate or Propecia for hair loss. Same molecule, two doses, two jobs - and both demand patience.
What does it treat?
Benign prostatic hyperplasia - the enlarged prostate behind urinary difficulty, frequency, and urgency - and male pattern hair loss, the gradual thinning at the hairline and crown in men.
How do you take it?
One tablet once a day, with or without food, at the same time every day. The timelines are long: for BPH, symptoms may take at least 6 months to improve; for hair loss, expect at least 3 months before any change and judge the result at 12 months - if nothing has improved by then, further treatment probably will not help. For hair, it only works while you take it: any regrowth is typically lost within 12 months of stopping. It controls BPH but does not cure it: keep taking it even when you feel well, and never stop without your doctor. Missed dose: this one is simple - skip it and continue the schedule. Never double up.
Side effects to know
- Common: inability to have or maintain an erection, decreased sexual desire, ejaculation problems including decreased volume, and pain in the testicles. MedlinePlus notes these can occur during treatment and after it is stopped - that possibility deserves a real conversation before starting.
- Serious - call your doctor immediately: changes in the breasts such as increased size, lumps, pain, or nipple discharge; allergic reactions with rash, itching, hives, swelling of the lips and face, or trouble breathing or swallowing; and new or worsening depression or thoughts about harming or killing yourself.
Who should not take it?
It is only for use in men, and the pregnancy rule is physical: women who are or may become pregnant must not touch broken or crushed finasteride tablets - the drug absorbs through skin and can harm a fetus. If that contact happens, wash the area with soap and water immediately and call a doctor. Flag liver disease and prostate cancer. It may decrease fertility in men. And know the trade-off data: taking finasteride may increase the risk of high-grade prostate cancer, the faster-growing type - MedlinePlus says to talk through that risk with your doctor directly.
When is it an emergency?
Trouble breathing or swallowing, or swelling of the face and lips, is a 911 call. New or worsening depression, or any thought of harming or killing yourself, is a same-day call to your doctor - and the 988 Suicide and Crisis Lifeline (call or text 988) is there any time you need it. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why can't pregnant women touch finasteride tablets?
Skin absorption. MedlinePlus warns that women who are or may become pregnant should not touch broken or crushed finasteride tablets - the drug passes through skin and can harm a male fetus's development. Whole tablets are coated and safe to handle; broken or crushed ones are the hazard. If contact happens, wash with soap and water immediately and call a doctor.
How long does finasteride take to work?
Months, not weeks. For an enlarged prostate, MedlinePlus says at least 6 months before symptoms improve. For hair loss, at least 3 months before any improvement, with the real verdict at 12 months - and no improvement by then means it probably will not help. This is a judge-it-in-a-year drug.
Will my hair come back if I stop finasteride?
The regrowth goes, not the other way around. MedlinePlus says finasteride only slows hair loss while you take it, and you will probably lose any hair that grew back within the first 12 months after stopping. Stopping is always your choice - just make it knowing the clock on the results runs backward.
Are the sexual side effects of finasteride permanent?
For most men they resolve, but MedlinePlus states plainly that decreased sexual desire, ejaculation problems, and erection problems may occur during treatment and after it is stopped, and that finasteride may decrease fertility. That is a risk to weigh before starting, not after - bring it up at the prescribing visit, and report any change early.
Does finasteride cause depression?
It is on MedlinePlus's serious list: new or worsening depression, or thoughts about harming or killing yourself, means calling your doctor immediately. Most men never see it, but it is real enough to make the list - if your mood shifts on this drug, treat it as a medication question, not a personal one. And 988 (call or text) is there anytime.
What happens if I miss a dose of finasteride?
Skip it and continue your regular schedule - MedlinePlus says do not take a double dose to make up for a missed one. This drug works by holding hormone levels down over months, so one missed tablet changes nothing. A pattern of misses is what lets the hormone come back.