These are clinical diets for diagnosed conditions, not premium cat food. They work by restricting or adjusting things a healthy cat needs, which is why they should only be fed on a vet's recommendation and why some are actively unsuitable for a well cat.
If your vet has named a diet, this page is where you reorder it. If they haven't, book an appointment rather than guessing from the symptoms.
Buy exactly what your vet named
Three brands here, and each names its diets differently, which is why matching the vet's note matters more than it looks.
Hills Prescription Diet uses two-letter codes: c/d for urinary, k/d for kidney, i/d for digestive, m/d for diabetes, t/d for dental, y/d for thyroid, and z/d for food sensitivities. Metabolic and Gastrointestinal Biome are named rather than coded.
Royal Canin Veterinary uses words: Urinary SO, Renal, Gastrointestinal, Sensitivity Control.
Pro Plan Veterinary Diets uses short abbreviations: UR for urinary, NF for renal function, EN for gastrointestinal, HA for hypoallergenic, OM for obesity management.
Similar-looking names are different foods. Hills c/d Multicare and c/d Urinary Stress are not interchangeable, and neither are Royal Canin Urinary SO and the ordinary Urinary Care recipe from the retail range.
Can you swap between brands?
Not without asking. Two diets for the same condition can work in genuinely different ways, particularly with urinary diets, where some are formulated to dissolve existing crystals and others to prevent them forming.
If the one your vet named is out of stock, ring the practice and ask what else they're happy with rather than picking the nearest-sounding alternative.
Feed it exclusively
Most of these diets only work if they're all your cat eats. Treats, a saucer of milk or a share of the other cat's food will undo a good part of the effect, and it matters most with the urinary, kidney and food sensitivity diets.
If you want to give your cat something extra, ask your vet what's allowed. Several brands make treats designed to go with their therapeutic ranges.
Wet as well as dry
Most of these come in both, and feeding some wet is worth doing for any cat with kidney or urinary trouble. Moisture intake matters as much as the formulation, and cats are poor drinkers.
It also helps with the bigger practical problem: a therapeutic diet the cat refuses is no use at all. If yours won't touch the kibble, try the wet version of the same diet before giving up on it.
Buy the small size first
These diets are dear and you can't return opened food. If your cat is starting something new, buy the smallest pack, find out whether they'll eat it, then order properly. Introduce it over a week or two mixed with the old food unless your vet has said otherwise.
One thing worth knowing: never try to wait a cat out. A cat that stops eating for more than a day or two can develop serious liver problems, and quickly. If yours refuses the new diet and won't be tempted back onto anything, ring your vet.
Supplements alongside
Some conditions are managed with a diet and a supplement together, particularly urinary and joint problems. Those sit under cat health next to the diets for each condition, so you can see the options in one place.