Please rule out hyperthyroidism and hypertension before going for the behavioral and using remedies. You'll just be spinning your wheels and wasting $ if it is medically based.

Good luck
Rose

From the internet:


Night-time yowling is a very common problem in older cats. Like many symptoms, it has multiple causes. Many older cats have more than one of the listed problems, so it is important to carefully consider the possibility of all of them in an affected cat.

Hyperthyroidism is the most commonly reported inducer of this behavior and is also the most likely medical cause in a cat that is on the young side when the behavior occurs. This is relatively easy to test for but it can take more than one test, in some instances, to confirm the diagnosis. Usually cats with hyperthyroidism have increased activity levels and are eating more but not gaining weight.

Hypertension (high blood pressure), normally associated with kidney failure, can cause night time yowling. Or at least treatment for hypertension sometimes decreases night time yowling --- it is hard to be sure that the medication doesn't have a beneficial effect separate from the lowering of blood pressure unless accurate blood pressure monitoring is done.

Cats appear to be affected by decreases in their ability to see and to hear in a manner that induces yowling at night. There is a theory that this produces anxiety and that yowling is the result. Some cats do respond to anti-anxiety medications such as diazepam (Valium Rx) or amitriptyline (Elavil Rx).

Cats also seem to get cognitive disorders similar to those experienced by dogs and humans, in which confusion, loss of orientation and other signs of decreased mental ability occur. This may lead to night time yowling, as well. The currently recommended treatment for this is to try selegiline (Anipryl RX). This medication isn't approved for cats (but then neither are diazepam or amitriptyline) and there is less proof that a condition responsive to it exists in cats than there is in dogs.