Tamsulosin (Flomax): how it helps urinary symptoms and side effects

By the Medsmingle Team · Updated 13 November 2026

This is a prescription medicine. Only take it if it has been prescribed for you, and follow your doctor’s and pharmacist’s instructions.

Tamsulosin (Flomax) is an alpha-blocker used to ease urinary symptoms of an enlarged prostate (BPH), such as a weak stream and needing to go at night. Doctors sometimes also use it to help pass kidney stones. See enlarged prostate (BPH).

How it works

It relaxes the muscles in the prostate and bladder neck so urine flows more easily. It doesn’t shrink the prostate.

How to take it

• Once a day, about 30 minutes after the same meal each day
• Swallow the capsule whole
• Improvement often starts within days, with full effect in 2 to 4 weeks

Side effects

• Dizziness or light-headedness, especially when standing up or after the first doses: stand up slowly
• Changes in ejaculation or semen volume; discuss persistent or concerning symptoms with your prescriber
• Stuffy nose, headache

Important warnings

• Cataract surgery: tell your eye surgeon you take or have taken tamsulosin, as it can affect the iris during surgery
• Fainting risk is higher with other blood pressure medicines or erectile dysfunction pills; ask your doctor about timing
• A painful erection lasting more than 4 hours (very rare) needs emergency care
• Rare sulfa allergy reactions

See a doctor if

Being unable to urinate needs urgent medical assessment. Also contact a clinician for blood in the urine or worsening symptoms.

Frequently asked questions

Can I take tamsulosin at night?

Follow the timing on your prescription. If you wish to change the meal or time, ask your pharmacist first.

Does tamsulosin affect fertility?

It can reduce semen volume, which may affect conception while taking it; discuss fertility concerns with your prescriber before changing treatment.

For questions about a prescription or symptoms, speak with your own doctor or pharmacist. For website enquiries, contact our team.

This article is for general information only and isn’t a substitute for advice from a doctor or pharmacist.

Source and further reading

MedlinePlus patient medicine information. This overview does not list every warning or interaction.