Why prescription diets only score in the sixes.

What a prescription diet actually is

A “prescription diet” or “therapeutic diet” is a specifically formulated food sold through a veterinarian for dogs with diagnosed medical conditions: kidney disease, pancreatitis, food allergy, obesity, hyperthyroidism, urolithiasis, and so on. In the U.S., these foods are not legally required to be prescription-only — that’s a manufacturer-and-channel convention. But all of them are designed around a clinical constraint that drives the entire recipe.

The k/d formula is built around reduced phosphorus and controlled protein to slow chronic kidney disease progression. HA Hydrolyzed is built around protein molecules broken below the size that triggers an immune response, for elimination-trial diagnostics and severely allergic dogs. y/d is built around severe iodine restriction as a non-surgical hyperthyroidism management option. The clinical objective is the formula. Everything else is downstream.

The full slate of prescription diet scores

Every prescription diet currently scored on PetScored, sorted by composite. The numbers are pulled live from the dataset, not curated for this article.

1. 01Hill's Prescription Diet i/d Digestive Care Chicken Flavor6.9
2. 02Hill's Prescription Diet w/d Multi-Benefit Chicken Flavor6.4
3. 03Royal Canin Veterinary Diet Hypoallergenic Hydrolyzed Protein Adult HP6.3
4. 04Purina Pro Plan Veterinary Diets OM Overweight Management6.2
5. 05Royal Canin Veterinary Diet Urinary SO Adult6.2
6. 06Purina Pro Plan Veterinary Diets EN Gastroenteric6.1
7. 07Hill's Prescription Diet k/d Kidney Care Original6.0
8. 08Purina Pro Plan Veterinary Diets HA Hydrolyzed5.9
9. 09Royal Canin Veterinary Diet Gastrointestinal Low Fat Adult5.9
10. 10Hill's Prescription Diet y/d Thyroid Care Chicken Flavor5.5

Where the points are lost

The composite is a weighted blend of five sub-scores. The two that pull prescription diets down are Ingredient Clarity (the rubric rewards short, named, recognizable ingredient panels) and Value (the rubric reports cost per 1000 kcal against a benchmark median for the category). Across the ten Rx diets, the average Ingredient Clarity sub-score is 7.3. The average Brand Trust sub-score is 6.0— the highest tier we have, because these are the same three brand families we covered in last week’s vet-channel editorial.

The Ingredient Clarity hit is structural. A renal diet substitutes egg product, corn starch, and refined fats for first-ingredient muscle meat because muscle meat is high in phosphorus. A hydrolyzed-protein diet substitutes hydrolyzed soy for intact animal protein because intact animal protein is what the dog’s immune system is reacting to. A high-fiber weight-loss diet leads with powdered cellulose because the goal is satiety with minimal calories. None of these are defects. They are the formula doing its job.

What our rubric is and isn’t designed to score

PetScored grades what the label can prove. We grade nutrient density against AAFCO benchmarks, ingredient specificity, brand transparency, sensitivity trigger exposure, and cost-per-calorie. None of those are therapeutic efficacy. A renal diet that successfully slows CKD progression is doing the thing the bag was designed to do, and that does not appear on our scorecard. We do not score whether the food is treating the disease.

This is on the methodology page under what we refuse to score: we will not tell a reader that a specific food treats or cures a specific condition. That would require clinical evidence we do not have and is the domain of a veterinarian who has examined the dog. The rubric reports what it can; it stays silent about what it can’t.

If your vet prescribed one of these

The honest read: don’t switch off a prescribed diet based on a composite score from a rating site. Not ours, not anyone’s. The vet has clinical data you don’t — bloodwork, urinalysis, biopsy results, response to past foods — and the dietary intervention is part of the treatment plan. If you have concerns, the right conversation is with the vet, not the rating site.

The other honest read: a 6.8 on our rubric is not a bad score. The all-brands average is around 6.8. Prescription diets cluster at or slightly above that average. They lose points specifically on ingredient elegance and price, which is what a therapeutic formula trades away by design.

What we’d like to see from the manufacturers

One change that would meaningfully lift prescription diet scores under our rubric without compromising clinical design: clearer published evidence that the specific recipe was tested in a feeding trial for its target condition. Most prescription diets carry AAFCO “formulated to meet” adequacy statements, not the stronger “Animal feeding tests using AAFCO procedures” statement. The pharmaceutical-grade safety case behind these formulas would lift Brand Trust scores another half-point. We hope the manufacturers publish more of that evidence over time.

— The PetScored desk. Reading a prescription diet bag right now? See the full per-recipe breakdown by clicking any product above.