Hill's splits into two ranges that look similar and aren't. Science Plan is everyday food anyone can buy. Prescription Diet is clinical nutrition for diagnosed conditions and should only be fed on a vet's say-so. The dog range covers more conditions than most people realise.
What the letter codes mean
Prescription Diet uses two-letter codes rather than names, which is baffling if nobody has explained it. Each letter is a mnemonic for what the diet is for:
- a/d Acute care, for recovery after illness or surgery
- b/d Brain, for cognitive decline in older dogs
- c/d Crystals, for urinary health and struvite management
- d/d Dermatology, for food sensitivities and skin
- g/d Geriatric, for senior maintenance
- h/d Heart, low sodium for cardiac support
- i/d Intestinal, for digestive and gastrointestinal problems
- j/d Joints, for mobility and cartilage
- k/d Kidney, for renal care
- l/d Liver, for hepatic care
- m/d Metabolic, for weight and glucose management
- r/d Reduction, for weight loss
- t/d Teeth, for dental care
- u/d Urinary, for non-struvite stones and kidney support
- w/d Weight, for maintenance after weight loss, plus glucose and fibre
- z/d For food sensitivities, using hydrolysed protein
Match the code on your vet's note exactly. Similar-looking codes are entirely different foods, and the variants matter too: i/d and i/d Low Fat are not interchangeable, and neither are c/d and u/d despite both being urinary.
d/d or z/d
Both are for food sensitivities and they work in opposite ways. d/d uses a single novel protein, on the basis that a dog that has never eaten it has nothing to react to. z/d uses hydrolysed protein, broken down small enough that the immune system doesn't recognise it. Your vet picked one for a reason, so don't swap because the other is in stock.
Science Plan, the everyday range
Puppy, adult and mature recipes with small and large breed versions, plus Perfect Weight, Sensitive Stomach & Skin and Oral Care. Ordinary complete foods, no vet needed.
Worth being clear: Science Plan Perfect Weight is not Prescription Diet Metabolic, and Sensitive Stomach & Skin is not d/d or z/d. The everyday versions are for dogs who could do with a nudge. The prescription ones are for dogs with a diagnosis.
Feeding a prescription diet properly
These work by restricting or adjusting things a healthy dog needs, which is why they aren't a general upgrade and some are unsuitable for a well dog.
Most are meant to be fed exclusively. Adding ordinary treats, chews or scraps undermines the point, and it matters most with the urinary, kidney and food sensitivity diets. If you want to give treats, ask your vet what's allowed rather than guessing.
Give it time. Most therapeutic diets need six to eight weeks before you can judge them, and stopping early because nothing has changed in a fortnight is the commonest mistake.
Wet as well as dry
Several prescription diets come in cans as well as bags, which matters if your dog is off their food. A therapeutic diet the dog refuses is no use, so if the kibble is being ignored, try the wet version of the same code before abandoning the diet.
When not to start here
If your vet hasn't named a diet, don't buy one. A dog drinking more than usual, losing weight or having recurring upsets needs an appointment, not a bag of food. If you're reordering what your vet already prescribed, that's exactly what this page is for, and the veterinary dog food page has the other brands alongside.