Adult cats barely meow at one another. The meow is a signal cats developed for communicating with people, which means a cat that is vocalising constantly is trying to tell you something.

Rule out medical causes first, especially in older cats

An older cat that starts calling loudly, particularly at night, needs examining before anything else. Three conditions account for most of these cases:

Hyperthyroidism. Common in cats over ten. Weight loss despite a good appetite, increased thirst, restlessness and night calling.

High blood pressure, often alongside kidney disease or thyroid disease. It can cause disorientation and sudden blindness, and a cat that cannot see calls out.

Cognitive dysfunction. The feline equivalent of dementia. The cat becomes disoriented, sleeps at the wrong times, and calls out at night into an empty room.

Pain from arthritis, and deafness, also produce vocalising. A deaf cat cannot hear its own voice and calls much louder.

Behavioural reasons

If medical causes are excluded:

Attention. The most common reason. If meowing has ever produced food, a door being opened or company, the cat has learned that it works. Responding intermittently teaches it more strongly than responding every time.

Hunger and routine. Cats have accurate internal clocks and will announce a late meal.

A cat in heat. An unspayed female in season calls loudly and persistently for days, and males will call in response. Neutering resolves it.

Boredom. Common in indoor only cats with nothing to do. Under-stimulated cats become vocal.

Stress. A house move, a new animal, building work, a change in the household.

What to do

Have an older cat checked first. Then, for a behavioural cause:

Do not respond to the meowing itself, and reward quiet instead. Expect it to get worse before it gets better; a behaviour that used to work gets tried harder before it is abandoned.
Keep feeding times consistent, and use a timed feeder if the calling is at dawn.
Add play. Two short sessions of hunting style play a day changes many vocal cats.
Add vertical space, window perches and food puzzles for indoor cats.
Neuter unneutered cats.

When to come in

Any cat over seven that has recently started vocalising more. Vocalising with weight loss, increased thirst, or changes in sleep. A cat that seems disoriented or bumps into things. Or crying that sounds like pain, especially in a male cat straining in the litter tray, which is an emergency.