Alpha-1 adrenoceptor blocker (selective for alpha-1a) Pregnancy: Tamsulosin is not indicated for use in women (§4.6). Ejaculation disorders — including retrograde ejaculation and ejaculation failure — have been observed in short and long term clinical studies and reported post-authorisation.

Tamsulosin

Brand names: Flomax MR, Stronazon MR

Tamsulosin is an alpha-1-adrenoceptor blocker used to relieve the lower urinary tract symptoms of benign prostatic enlargement.

Adult dose

Dose: One 400 microgram prolonged-release tablet

Route: Oral

Frequency: Once daily

SOURCE: eMC UK SPC, 'Faramsil 400 microgram Prolonged-release Tablets', §4.2, which states in full: 'One tablet daily can be taken independently of food' — the 400 microgram strength is the strength of the fetched product; the SPC posology itself is expressed only as 'one tablet daily'. ADMINISTRATION: swallow the tablet whole; it should not be crushed or chewed as this will interfere with the prolonged release of the active ingredient. SPECIAL POPULATIONS: no dose adjustment in renal impairment, or in mild to moderate hepatic impairment (severe hepatic insufficiency is a contraindication). PAEDIATRICS: safety and efficacy in children under 18 years have not been established. SURGERY: intraoperative floppy iris syndrome (IFIS) has been observed during cataract and glaucoma surgery — initiation in patients scheduled for cataract or glaucoma surgery is not recommended, and surgeons/ophthalmic teams should be told at pre-operative assessment if the patient is taking or has taken tamsulosin. US labelling (cross-check, tamsulosin hydrochloride capsules): 0.4 mg once daily approximately one half-hour after the same meal each day; may be increased to 0.8 mg once daily in patients who fail to respond after 2 to 4 weeks; if therapy is interrupted for several days, restart at 0.4 mg once daily.

Dose adjustments

Renal

No dose adjustment is required in patients with renal impairment. Treatment of patients with severe renal impairment (creatinine clearance less than 10 ml/min) should be approached with caution, as these patients have not been studied (§4.4).

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Tamsulosin hydrochloride capsules 0.4 mg once daily is recommended as the dose for the treatment of the signs and symptoms of BPH. It should be administered approximately one-half hour following the same meal each day. Tamsulosin hydrochloride capsules should not be crushed, chewed or opened. For those patients who fail to respond to the 0.4 mg dose after 2 to 4 weeks of dosing, the dose of tamsulosin hydrochloride capsules can be increased to 0.8 mg once daily. Tamsulosin hydrochloride capsules 0.4 mg should not be used in combination with strong inhibitors of CYP3A4 (e.g., ketoconazole) [see Warnings and Precautions (5.2)]. If tamsulosin hydrochloride capsules administration is …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-01-01. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to tamsulosin, including drug-induced angio-oedema, or to any of the excipients
A history of orthostatic hypotension
Severe hepatic insufficiency

Side effects

Ejaculation disorders including retrograde ejaculation and ejaculation failure (common; abnormal ejaculation was the most commonly reported reaction, approximately 2% of patients)
Dizziness (common, 1.3%); headache (uncommon); syncope (rare); asthenia (uncommon)
Orthostatic hypotension and palpitations (uncommon); post-marketing: atrial fibrillation, arrhythmia, tachycardia, dyspnoea
Rash, pruritus, urticaria (uncommon); angioedema (rare); Stevens-Johnson syndrome (very rare); erythema multiforme and exfoliative dermatitis (not known)
Nausea, vomiting, constipation, diarrhoea, rhinitis (uncommon); blurred vision and visual impairment (not known); intraoperative floppy iris syndrome during cataract and glaucoma surgery; priapism (very rare)

Interactions

Strong CYP3A4 inhibitors — must not be given in patients with poor metaboliser CYP2D6 phenotype; use with caution with strong and moderate CYP3A4 inhibitors (§4.4)
Cimetidine increases and furosemide lowers plasma levels of tamsulosin; as levels remain within the normal range, the posology need not be changed
No interactions were seen when tamsulosin was given with atenolol, enalapril or theophylline
NOTE: eMC §4.5 was truncated at the source-fetch limit ('In vitro, neither diazepam nor …') — the clinician must verify the full interaction list. US labelling adds: caution with strong (e.g. paroxetine) or moderate (e.g. terbinafine) CYP2D6 inhibitors and in known CYP2D6 poor metabolisers; concomitant PDE5 inhibitors can potentially cause symptomatic hypotension; should not be used with other alpha-adrenergic blocking agents

Clinical monograph

How it works

It selectively blocks α1-adrenoceptors in prostatic and bladder-neck smooth muscle, reducing outflow resistance.

Prescribing in practice

Postural hypotension and dizziness can occur, particularly with the first dose.
It causes intra-operative floppy iris syndrome — patients must tell the ophthalmologist before cataract surgery.
Use caution with other blood-pressure-lowering drugs and PDE5 inhibitors.

Monitoring

Review symptom response and postural blood pressure.

Counselling the patient

The first dose may cause dizziness — take care when standing up.
Tell your eye surgeon you take it before any cataract operation.
It can cause changes to ejaculation.

Evidence & guidelines

Alpha-blockers are first-line for moderate-to-severe lower urinary tract symptoms due to benign prostatic enlargement, per NICE NG97.

Reference: NICE NG118 Lower Urinary Tract Symptoms; EAU Urology Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways