Flomax vs finasteride for an enlarged prostate: compared
Flomax (tamsulosin) and finasteride (Proscar) both treat urinary symptoms from an enlarged prostate, but in different ways. Tamsulosin relaxes the prostate muscle and works within days; finasteride slowly shrinks the prostate over months and lowers the chance of needing surgery.
Updated October 4, 2026
At a glance
- How it works
- Flomax
- Relaxes muscle in the prostate and bladder neck
- Finasteride
- Shrinks the prostate by lowering DHT
- How fast
- Flomax
- Within days
- Finasteride
- Six months or more
- Long-term benefit
- Flomax
- Symptom relief
- Finasteride
- Lowers the risk of urinary retention and surgery
- Common side effects
- Flomax
- Dizziness, ejaculation changes
- Finasteride
- Lower sex drive, erection changes
- Generic
- Flomax
- Yes
- Finasteride
- Yes
Flomax tamsulosin, an alpha blocker | Finasteride Proscar, a 5-alpha reductase inhibitor | |
|---|---|---|
| How it works | Relaxes muscle in the prostate and bladder neck | Shrinks the prostate by lowering DHT |
| How fast | Within days | Six months or more |
| Long-term benefit | Symptom relief | Lowers the risk of urinary retention and surgery |
| Common side effects | Dizziness, ejaculation changes | Lower sex drive, erection changes |
| Generic | Yes | Yes |
Fast relief or long-term change
Tamsulosin eases a weak stream, hesitancy and frequent urination quickly, which makes it a common first treatment. Finasteride works only when the prostate is enlarged, takes months, and is most useful for larger prostates, where it shrinks the gland and lowers the long-term risk of being unable to pass urine or needing surgery. For larger prostates, the two are often taken together.
Things to know
Tamsulosin can cause dizziness on standing, especially with the first doses or with erectile dysfunction medicines; tell your eye surgeon you take it before cataract surgery, even if you have stopped. Finasteride roughly halves the PSA blood test result, so tell whoever checks your PSA, and anyone who is or may become pregnant should not handle crushed or broken tablets.
Taking them
Tamsulosin is taken once a day about 30 minutes after the same meal, and restarted at the lowest dose after a break of several days. Finasteride is taken once a day with or without food.
Cost
Both are inexpensive generics, and 90-day supplies usually cost less per day.
When to see a clinician sooner
Urinary symptoms can have causes other than an enlarged prostate, so they are assessed before treatment starts. Seek care promptly if you cannot pass urine at all, see blood in your urine, or have fever or pain when urinating, which need checking rather than waiting for a medicine to work.
Questions for your prescriber
- Is my prostate large enough for finasteride to help?
- Would taking both work better for me?
- How will this affect my PSA tests?
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Sources
Written by the Script Unlock editorial team from the sources above. It is general information, not advice for you or your pet; your prescriber decides which medicine is right.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.