specifically developed for management of specific medical problems. Some of the diets are formulated differently enough from a "maintenance" or "growth" type diet that they are INAPPROPRIATE or UNSAFE in animals that do not have the medical condition. For example, I am always careful to caution people not to put K/D (kidney diet) out if they have kittens in the home. You CANNOT raise a healthy kitten on a renal diet, because it is protein-restricted and kittens have a very specific protein requirement.

Also, if you have a cat that is prone to calcium oxalate urinary stones, it is critical that it not have access to a diet that acidifies urine (like C/D or S/D) because acidic urine PROMOTES formation of oxalate stones.

There are many examples of this sort of thing. We put cats on prescription diets when they have a medical condition tht requires monitoring and followup, so we don't sell them OTC to just anybody who walks in the door. The potential for harm is there. Hill's Prescription Diets and the other brands of medical diets have a statement on the label something like: for temporary use as recommended by your veterinarian. This is different from the statement of nutritional adequacy on regular food that should say somethin like: Provides complete and balanced nutrition for growing kittens (or adult cats, or senior cats) based on AAFCO protocol feeding trials.

Some prescription diets (like S/D) we use ONLY short term, to dissolve struvite uroliths, and NOT for long-term maintenance. Other prescription diets we use for the life of the animal. But it always requires ongoing veterinary supervision in case the animal's needs change and the diet becomes inappropriate.