Dutasteride: what it treats, how to take it, side effects
Last updated September 3, 2026.
Dutasteride is a 5-alpha reductase inhibitor - it blocks production of the natural substance that enlarges the prostate. You may know it as Avodart. It shrinks the gland slowly, over months, and it comes with handling rules most pills do not need.
What does it treat?
Benign prostatic hyperplasia - the enlarged prostate behind the weak stream, the hesitation, the dribbling, and the 2 am bathroom trips.
How do you take it?
One capsule once a day, with or without food, same time daily. Swallow whole - never open, chew, or crush; the contents can irritate your mouth and throat. Improvement builds over months, not days, so patience is structural. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: inability to have or maintain an erection, decreased sex drive, and ejaculation problems - the hormone trade, worth naming out loud because it drives many silent quits.
- Serious - call your doctor immediately or get emergency help: breast changes - enlargement, lumps, pain, or nipple discharge; swelling of the face, tongue, or throat; difficulty breathing or swallowing; and peeling skin.
Who should not take it?
It is for men - women and children must never take it, and pregnant or potentially pregnant women must not even handle leaking capsules, because the absorbed drug can harm a male fetus. The cancer conversation belongs up front: dutasteride may increase the risk of high-grade prostate cancer - discuss it with your doctor. It also lowers PSA test results, so every PSA on this drug is interpreted against that fact. If you donate blood, you are deferred while on it and for months after.
When is it an emergency?
Tongue or throat swelling, trouble breathing, or peeling skin is emergency care. 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 handle the capsules?
The drug blocks a hormone a male fetus needs for normal development - and it absorbs through skin from a leaking capsule. MedlinePlus bars women who are or may become pregnant from handling it, and children from taking it at all. Household rule: the bottle stays his, capsules intact, and anything leaking gets washed off skin immediately with soap and water.
Why did my doctor talk about prostate cancer when prescribing a BPH drug?
Two reasons. First, dutasteride may increase the risk of high-grade prostate cancer - rare, but MedlinePlus says to discuss it. Second, it lowers PSA results by roughly half, which can mask a rising PSA. The response is not fear but calibration: baseline PSA before starting, and every later result interpreted as the on-drug number.
Why does it take months to work?
It shrinks the gland by changing hormone signaling - tissue remodels slowly. Where alpha-blockers relax the prostate's muscle within days, dutasteride physically reduces the obstruction over 3 to 6 months or more. Many men start on both: the alpha-blocker for now, the dutasteride for later, sometimes dropping the first once the second has done its work.
Why did it affect my sex drive?
Same hormone mechanism that shrinks the prostate - erectile difficulties, decreased libido, and ejaculation changes are the labeled common effects. For many men they are mild or fade; for some they persist. Say it out loud at appointments: dose questions, drug alternatives, and the stop-start trade-offs are all discussable. Suffering silently and quitting alone is the pattern that ends in the urologist's office anyway.
Why can't I donate blood while taking it?
Your blood could go to a pregnant woman, and the drug in it could harm a male fetus - so donation is off while you take dutasteride and for months after stopping (the drug lingers). It is one of the few medications with a formal blood-donation deferral, and it is about the recipient, not you.
What happens if I miss a dose of dutasteride?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. The drug's effect builds and decays over weeks, so a single missed capsule is invisible. The same-time-daily habit is what keeps the slow engine running.