A cat that keeps visiting the litter box and produces almost nothing is having an emergency, not a behaviour problem. Urethral obstruction — most often in male cats — blocks the outflow of urine, and the bladder keeps filling. Within a day or two, potassium rises to levels that stop the heart, and the kidneys begin to fail. This is one of the few feline conditions where a delay of a few hours genuinely changes the outcome. If a male cat is straining and no urine is coming out, go to a vet now, including at night.

Why male cats block so easily

The male urethra is long, narrow, and curves at the tip, which makes it a natural bottleneck. Obstruction usually comes from a plug of mucus, protein, and crystals, sometimes with small stones, and it is often laid down on top of inflammation of the bladder (cystitis). Stress, low water intake, dry food only, obesity, and indoor confinement all raise the risk. Some cats block repeatedly, and each episode does more damage to the bladder and kidneys. Female cats can block too, but far less often; their signs are easier to miss.

The signs, roughly in the order they appear

Early: trips to the litter box far more often than usual, posturing to urinate for a long time, small or no result, licking the penis or vulva repeatedly, and urine found outside the box. Owners often describe "constipation" at this stage. Next: crying or yowling while straining, restlessness, pacing, and a bladder that feels hard and marble-like through the belly wall — though you should not press on it. Later: appetite loss, vomiting, weakness in the back legs, disorientation, breathing changes, collapse. A cat at that stage may look calm, which is often mistaken for improvement.

How fast it becomes life-threatening

Most veterinary references put the dangerous window at 24 to 48 hours after complete obstruction. Some cats deteriorate faster, particularly if they are already dehydrated or have kidney disease. The mechanism is predictable: urine backs up, the bladder distends and can rupture, potassium accumulates and disrupts the heartbeat, and acute kidney injury develops. Cats that survive an episode still need monitoring for days, because post-obstruction diuresis can cause severe dehydration and electrolyte shifts.

Blockage, cystitis, or constipation?

Cystitis (inflammation without obstruction) causes frequent, painful, small urinations, sometimes with blood, but urine does flow. Constipation causes straining with hard, dry stool and often no urine at all in the box — check the box for stool as well as clumps. If you are unsure, assume blockage: it is the one that kills. A vet can tell within minutes by palpating the bladder and, if needed, taking an X-ray or ultrasound. Never assume "he is just stressed" in a male cat that has produced no urine for 12 hours.

What to do right now

Call the clinic while you are getting the carrier out, and say clearly: male cat, straining, little or no urine. Go in, even if it is 2 a.m. Do not wait to see whether he passes urine overnight. Bring the litter box history — when you last saw a normal clump — because the timeline changes triage. If the cat is vomiting or collapsed, say so on the phone. Keep him confined and calm; do not let him outside, where he may hide and die under a neighbour's deck.

What not to do

Do not press or squeeze the bladder; a full bladder can rupture. Do not give cranberry supplements, apple cider vinegar, or human urinary remedies — none of them relieve an obstruction. Do not restrict water, and do not assume adding water to dry food will fix a cat who is already blocked. Do not give painkillers from the cabinet. Do not accept a "wait and see" plan for a male cat with no urine output, and do not let a phone assessment replace an examination if the cat is straining.

When to go immediately (do not wait for morning)

  • Straining in the litter box with no urine, or only drops, for more than a few hours.
  • Repeated trips in and out of the box, with yowling.
  • A hard, enlarged, painful bladder — the belly feels tight like a small balloon.
  • Vomiting, refusing food, or sudden lethargy in a cat with urinary signs.
  • Weakness in the hind legs, wobbling, or collapse.
  • Blood in the urine with straining.
  • Any male cat with no urine for 12 hours, whatever else looks normal.

Treatment and prevention after the episode

A vet will relieve the obstruction with a urinary catheter under sedation, flush the bladder, and run fluids to correct potassium and dehydration. Most cats stay in hospital for one to three days on a catheter with a collection system, and are monitored for re-blockage after removal. Long-term prevention is unglamorous but effective: wet food or a mixed diet to increase water intake, multiple water bowls or a fountain, a low-stress indoor environment with enough resources, weight control, and prompt treatment of cystitis. Prescription urinary diets help when crystals or stones are documented. Cats who block once are at real risk of blocking again — a recurrence plan agreed with your vet is part of the treatment, not an optional extra. For feeding and water strategies, see care, and for the wider picture of feline urinary disease, health.

This is general information, not a diagnosis.

Frequently asked

How long can a blocked cat survive without treatment?

Usually 24 to 48 hours before potassium and kidney failure become life-threatening, and some cats deteriorate faster. There is no safe period to wait at home. A male cat with no urine for 12 hours should be examined immediately.

Can a cat be blocked and still produce a few drops of urine?

Yes. Partial or intermittent obstruction can let small amounts through, which is why owners sometimes wait. Any male cat that strains repeatedly with only drops, or urinates outside the box with effort, needs same-day veterinary assessment.

Does switching to wet food prevent blockage?

It reduces risk by raising water intake and diluting urine, but it does not guarantee prevention. Cats with documented crystals or stones often need a prescription diet, and stress reduction and weight control matter too. A cat that has blocked once needs a recurrence plan.