Acute Urinary Retention in Men: Why Does This Happen?

Dernière mise à jour : août 29, 2026

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Acute urinary retention — being suddenly unable to pass urine despite a full bladder — is one of the true urological emergencies. It is far more common in men than in women, which is why this article focuses on men, and it is commonest in those over 60.

If this is happening to you right now: being unable to pass urine while the bladder feels painfully full needs treatment the same day — go to an emergency department rather than waiting to see whether it eases. The bladder can only stretch so far, and prolonged over-distension damages both the bladder muscle and, eventually, the kidneys. Draining it is quick and brings immediate relief. In Thailand, call 1669.

Symptoms That Need Attention the Same Day

• Being unable to pass urine at all, with a painful, full lower abdomen.
• Fever or shaking chills alongside difficulty passing urine.
• Passing only small amounts frequently, with constant dribbling. This is easily mistaken for the problem improving, or for ordinary incontinence. It can instead be a full, obstructed bladder overflowing — the bladder is not emptying at all, and the leakage is the overflow. It needs assessment rather than reassurance.
• New weakness or numbness in the legs, numbness around the buttocks, genitals or inner thighs, or loss of bowel control together with retention. This suggests pressure on the nerves at the base of the spine and is an emergency measured in hours, not days.
• A catheter that stops draining, if you already have one.

This article explains the causes. If a trigger set off the episode — and one often does — the companion article on the reversible causes of sudden inability to pass urine covers what happens after the catheter goes in and how the trigger is found.

Causes that block the outflow

1. Benign prostatic hyperplasia (BPH) — the commonest cause, and one no ageing man can entirely avoid. The prostate enlarges and compresses the urethra, typically producing a gradually weakening stream from the age of 50 onwards. Treating BPH properly reduces the risk of ending up in retention later; the two classes of prostate medication and the procedural options are covered separately.
2. Rétrécissement de l'urètre — a previous urethral infection, sexually transmitted infection or endoscopic urological procedure can leave scar tissue that narrows the urethral lumen until it obstructs.
3. Pierre urétrale — uncommon, but a stone lodged in the urethra blocks it completely and needs emergency removal.

Causes that stop the bladder emptying

4. Medications. Several drug classes impair bladder contraction or increase resistance at the outlet. The one worth knowing about above all others is the decongestant in ordinary cold and flu remedies — pseudoephedrine or phenylephrine — because it tightens the bladder outlet, it is bought without a prescription, and in a man with an enlarged prostate it is a classic cause of a first episode of retention. The older sedating antihistamines in the same remedies add to the effect. Also implicated: anticholinergic drugs (including some bladder medicines for an overactive bladder, and some anti-nausea and Parkinson’s medicines), tricyclic antidepressants, opioid painkillers, general anaesthesia, and a heavy episode of drinking. When the responsible drug is stopped, the retention often resolves on its own. Do not stop a prescribed medicine on your own — tell the doctor treating you everything you take, including anything bought over the counter, and let them decide.
5. Neurological causes — the nerve supply to the bladder can be disrupted at several levels. These cases are more complex and need careful urological assessment. Retention accompanied by numbness around the groin, buttocks or inner thighs, new weakness in the legs, or loss of bowel control is a different and far more urgent problem, and needs emergency assessment within hours.
6. Bladder dysfunction — the bladder muscle itself contracts poorly and simply fails to empty. This matters more than its position on the list suggests, because an underactive bladder produces almost the same picture as an obstructed outlet, and operating on the prostate of a man whose bladder is the real problem does not help him. The distinction is made with flow testing, residual urine measurement and, where it matters, pressure studies.

Contributing factors worth knowing about

7. Infection — a infection de la vessie, infection de la prostate or urethral infection causes enough local irritation and swelling to tip someone into retention. Acute prostatitis in particular can cause it outright. Fever together with retention needs urgent attention rather than a routine appointment.
8. Constipation — stool impacted in the rectum presses on the bladder outlet and obstructs flow. It is a surprisingly common cause, and one of the easiest to correct. Worth asking about in anyone immobile or taking opioids, since those cause constipation and retention at the same time.
9. Limited mobility, illness and recent surgery — voiding is under brain control and normally happens standing, in privacy. Bed rest, a general anaesthetic, post-operative pain relief and an unfamiliar environment combine, which is why retention is so common in hospital. Some patients improve simply by being helped to stand. It is also why an episode that happens in hospital does not automatically mean the prostate needs treating.

What happens in the emergency room

The first step is always bladder decompression — draining the retained urine with a urethral catheter, or a suprapubic tube where the urethral route is not possible. This relieves the pain immediately and protects the bladder from the damage that prolonged over-distension causes. Definitive treatment then follows once the cause is identified, and it differs completely depending on which of the nine causes above is responsible.

Two things are worth knowing in advance about what follows the drainage.

• Some blood in the urine is common after a large volume is drained. It happens because the bladder wall decompresses suddenly, it is usually self-limiting, and it settles within a day or two. Knowing that beforehand saves a great deal of unnecessary alarm.
• Occasionally the kidneys then produce a great deal of urine for a day or two. This is called post-obstructive diuresis, and it is usually defined as passing more than 200 ml an hour for two hours running, or more than three litres in a day. In most men it settles within about 24 hours and needs nothing more than watching. Where it continues beyond about 48 hours it becomes a problem in its own right, because losing that much fluid and salt can drop the blood pressure and disturb the body’s chemistry — which is a legitimate reason a man may be kept in hospital on fluids and blood tests rather than sent home with a bag. The heaviest diuresis, several litres a day and occasionally far more, generally happens only when both kidneys, or a single functioning kidney, were completely obstructed.

The volume drained is recorded, and it is worth being honest about what that number does and does not tell you. A very large volume does suggest the bladder had been struggling for a long time rather than failing suddenly. But there is no agreed volume above which retention is officially chronic: the formal definitions are based on how much urine is left after passing water rather than on how much comes out through the first catheter, and even those differ between guidelines — one uses more than 300 ml on at least two occasions over six months, while another sets the mark at a litre. Whether things settle down afterwards is predicted better by the kidney function, by whether the kidneys are swollen on a scan and by repeated infections than by the number on the drainage bag.

Kidney function is therefore checked, since obstruction affects it. And a medication to relax the bladder outlet is usually started before the catheter is removed, which makes a real difference: pooled trial data show roughly 60% of men pass urine successfully after the catheter comes out when an alpha-blocker has been given, against roughly 38% without one — and it also reduces the chance of going back into retention afterwards. That is one of the better-supported small interventions in urology, and it is a reasonable thing to ask about if it has not been mentioned.

Whether a prostate operation follows depends on what is found. Where a clear trigger is identified and removed — a cold remedy, constipation, an infection, an anaesthetic — many men pass urine normally once the catheter comes out and need nothing further. Where no trigger is found, retention tends to recur and the underlying obstruction usually needs treating; the options are set out on the enlarged prostate page.

If you or a loved one has experienced acute urinary retention or suspect BPH with worsening urinary symptoms, Dr. Soarawee Weerasopone offers specialist consultations at Hôpital de Bangkok Siège social. Appointments at Samitivej Sriracha Hospital in Chonburi can be arranged by calling the Urology department on 088-022-1445. Bring a list of everything you take, including cold remedies and anything bought without a prescription, and the record of how much was drained if you have it.

Bangkok Hospital Telemedicine is available for follow-up and non-urgent consultations, including for international patients — arrange it in advance by email to the Urology department at bhquro@bdms.co.th. Samitivej Sriracha is in-person only. Enquiries about cost are answered by the hospital rather than through this website. If you cannot pass urine now, go to hospital rather than emailing.

Foire aux questions sur la rétention urinaire aiguë chez l'homme

Références

• Fisher E, Subramonian K, Omar MI. The role of alpha blockers prior to removal of urethral catheter for acute urinary retention in men. Cochrane Database Syst Rev. 2014;(6):CD006744.
• Karavitakis M, Kyriazis I, Omar MI, et al. Management of urinary retention in patients with benign prostatic obstruction: a systematic review and meta-analysis. Eur Urol. 2019;75(5):788–798.
• Stoffel JT, Peterson AC, Sandhu JS, et al. AUA white paper on nonneurogenic chronic urinary retention: consensus definition, treatment algorithm, and outcome end points. J Urol. 2017;198(1):153–160.

Avis de non-responsabilité : This content is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters. It is intended for general education only and does not constitute medical advice, diagnosis or treatment for any individual. Being unable to pass urine with a painfully full bladder is a medical emergency — attend an emergency department the same day. Do not stop or change a prescribed medication without speaking to the doctor who prescribed it. No advice, diagnosis or prescription is given through personal messaging channels or social media, and Dr. Soarawee operates no public social media account. Always consult a qualified doctor about your own symptoms. In an emergency in Thailand, call 1669.