My cat keeps going in and out of the litter box, crying and straining, and nothing comes out — is he constipated?

Stop reading and take him to a vet or an emergency clinic right now, tonight — a male cat who is straining and producing no urine is very likely blocked, and a blockage kills.

A blocked cat cannot empty his bladder. The potassium rises in his blood, his heart slows, and it can kill him in roughly one to two days, with the last few hours coming on suddenly. This is almost certainly not constipation. The crying in the box, the licking, the going in and out, the vomiting and the hiding all fit a blockage.

When you call, use these words: “male cat, straining, no urine, possible blockage.” That phrase gets him triaged ahead of the queue instead of booked for tomorrow. Do not wait for morning and do not wait for your regular vet to open.

Do not press or squeeze his belly — a blocked bladder can tear. Put him in the carrier and go. On the way, try to remember the last time you saw a wet clump in the litter and tell the team; it helps them judge how long he has been blocked.

Female cats block far less often, but they do block. A straining female producing no urine goes in too.

The good news is that treatment works well when it happens early: sedation, a urinary catheter to relieve the bladder, fluids and monitoring. Cats who arrive in time usually go home. What he needs is decided by the exam and the bloodwork, not by a guess from a distance. The cost of being wrong about “he's probably just constipated” is his life. Go now.