Affiliate disclosure: HappyHealthyCat.com participates in the Amazon Associates program. When you click our links and make a purchase, we may earn a small commission at no extra cost to you. We only recommend products we genuinely believe help cats.
Your vet has just recommended a prescription urinary diet for your cat. You go home, search online, and immediately find yourself staring at two names that appear on every list: Hill’s Prescription Diet c/d and Royal Canin Urinary SO. Both are vet-recommended. Both are widely available. Both cost considerably more than regular cat food. So which one do you actually buy?
The honest answer is that both are excellent diets — but they work through slightly different mechanisms, suit slightly different situations, and perform differently in the one area that matters most practically: whether your cat will actually eat them. This comparison covers everything you need to make a confident decision.
- Best for struvite crystals and stress-related FLUTD: Hill’s c/d Multicare Stress — the added tryptophan addresses stress cystitis directly
- Best for mixed crystal types (struvite AND oxalate risk): Royal Canin Urinary SO — the only diet proven to reduce both
- Best palatability for fussy cats: Royal Canin Urinary SO — consistently rated higher by owners of reluctant eaters
- Best if your vet specifically recommended one: use that one — their recommendation is based on your cat’s specific urine test results
What These Diets Are Actually Trying to Do
Before comparing ingredients and prices, it helps to understand what urinary prescription diets are designed to achieve. Both Hill’s c/d and Royal Canin Urinary SO work toward the same three goals, using slightly different approaches:
- Dilute the urine — more dilute urine means lower mineral concentration, which reduces crystal formation risk. Both diets encourage higher water intake through increased sodium (which stimulates thirst) and are best fed as wet food for maximum moisture.
- Modify urine pH — struvite crystals form in alkaline urine. Both diets acidify urine to a range where struvite cannot form or persist. Calcium oxalate crystals form in acidic urine, so there is a careful balance to maintain.
- Control specific minerals — magnesium, phosphorus, and calcium are restricted to reduce the building blocks available for crystal formation.
Where they diverge is in their specific technology, their approach to oxalate crystal prevention, and their additional functional ingredients.
Hill’s Prescription Diet c/d Multicare: Overview
Hill’s c/d has been one of the most widely prescribed urinary diets for cats for decades. The “c/d” stands for “crystal/dissolution” — it was originally developed to dissolve struvite crystals and prevent their recurrence. The Multicare version addresses the most common causes of FLUTD together in one diet.
Key ingredients and mechanism
Hill’s c/d works primarily through mineral control and pH management:
- Restricted magnesium — reduces struvite formation directly, as magnesium ammonium phosphate (struvite) requires magnesium as a key component
- Controlled phosphorus and calcium — reduces both struvite and oxalate building blocks
- Urine acidification — maintains urine pH at 6.2–6.4, the range where struvite cannot form
- High moisture content (wet) — 78% moisture in the wet formula, significantly diluting urine
- Omega-3 fatty acids (EPA + DHA) — anti-inflammatory support for the bladder lining
The Stress variant — a meaningful difference
Hill’s c/d comes in two versions: regular Multicare and Multicare Stress. The Stress version adds L-tryptophan and hydrolysed casein — two ingredients with evidence for reducing anxiety in cats. This matters because feline idiopathic cystitis (FIC), the most common form of FLUTD, is directly linked to stress. For cats whose urinary episodes are triggered by anxiety, household changes, or environmental stressors, c/d Stress addresses a root cause that regular c/d does not touch.
If your cat’s urinary episodes seem linked to stressful events — a house move, a new pet, changes in your schedule — ask your vet specifically about Hill’s c/d Multicare Stress rather than the regular version. The stress-modulating ingredients can make a meaningful difference for cats with idiopathic cystitis.
Crystal coverage
Hill’s c/d is primarily formulated for struvite prevention and dissolution. It is effective for struvite but provides less specific protection against calcium oxalate crystals compared to Royal Canin Urinary SO. If your cat has been diagnosed specifically with struvite, or if stress cystitis is a factor, c/d is a strong choice.
Royal Canin Urinary SO: Overview
Royal Canin Urinary SO was developed with a specific technological focus: creating a urine environment where neither struvite NOR calcium oxalate crystals can form. The “SO” in the name stands for Struvite and Oxalate — communicating this dual-crystal approach directly.
Key ingredients and mechanism
- Relative Super-Saturation (RSS) technology — this is Royal Canin’s proprietary system. Rather than simply controlling individual minerals, RSS measures the overall saturation of the urine with respect to both struvite and calcium oxalate. The goal is to keep urine below the saturation threshold for both crystal types simultaneously.
- High sodium content — intentionally increases thirst, driving higher water intake and more dilute urine
- Controlled calcium and oxalate — reduces the building blocks for oxalate crystals specifically
- Urine acidification — maintains pH in the safe zone for struvite prevention
- Urine dilution focus — the RSS approach prioritises dilution as the primary protective mechanism
Crystal coverage
Royal Canin Urinary SO is the only urinary diet validated to reduce the risk of both struvite and calcium oxalate crystals. This makes it the preferred choice when the crystal type is uncertain, when a cat has had oxalate stones previously, or when a vet wants one diet to address the broadest possible urinary risk profile.
Struvite crystals form in alkaline urine and can be dissolved with diet in 4–8 weeks. Calcium oxalate crystals form in acidic urine and cannot be dissolved — if they form stones large enough, surgery is required. A diet that acidifies urine too aggressively can dissolve struvite but inadvertently increase oxalate risk. Royal Canin Urinary SO’s RSS technology is specifically designed to navigate this balance.
Head-to-Head Comparison
| Factor | Hill’s c/d Multicare | Royal Canin Urinary SO |
|---|---|---|
| Primary mechanism | Mineral control + urine acidification | RSS technology + urine dilution |
| Struvite protection | ✅ Excellent — can dissolve existing crystals | ✅ Excellent |
| Oxalate protection | ⚠️ Partial — not the primary focus | ✅ Excellent — validated for both types |
| Stress/FIC support | ✅ Yes (Stress variant only) | ❌ No specific stress ingredients |
| Wet food moisture | ~78% | ~82% |
| Typical price (wet) | $3.50–$4.50 per can | $3.00–$4.00 per can |
| Palatability (owner reports) | Good — most cats accept readily | Very good — higher acceptance in fussy cats |
| Available formats | Wet (pâté, minced, flaked) + dry | Wet (loaf, slices in gravy) + dry |
| Prescription required | Yes | Yes |
| Best suited for | Struvite, FIC, stress-related FLUTD | Mixed crystal risk, oxalate history, fussy eaters |
| Vet recommendation frequency | Very commonly prescribed | Very commonly prescribed |
| Available online | ✅ Yes (Rx) | ✅ Yes (Rx) |
Palatability: The Factor That Actually Determines Success
A perfect urinary diet that your cat refuses to eat is worthless. Palatability is arguably the most practically important factor when choosing between these two foods — and it is the area where Royal Canin Urinary SO consistently edges ahead in owner reports.
Both foods are formulated to be palatable, and both are accepted by the majority of cats without issue. However, in online forums, vet reviews, and owner communities, a pattern emerges: cats who reject Hill’s c/d often accept Royal Canin Urinary SO, and vice versa. Individual preference varies enormously.
Tips for the reluctant eater
- Warm the food slightly (10–15 seconds in the microwave, always check temperature) — this releases aroma and increases appeal
- Mix with a tiny amount of FortiFlora probiotic powder — it improves palatability of any food
- Transition slowly over 10–14 days for cats with urinary issues — their digestive systems are often sensitive
- Try the opposite brand if your cat refuses the first choice — most vets have samples they can provide before you buy a case
- Royal Canin Urinary SO comes in both loaf and slices-in-gravy formats — the gravy version appeals strongly to cats who prefer softer textures
Hill’s Prescription Diet c/d Multicare
Best for: struvite crystals, stress cystitis, FIC
Royal Canin Urinary SO
Best for: mixed crystal risk, oxalate history, fussy eaters
Price Comparison
Both diets are significantly more expensive than regular cat food, which surprises many owners. The cost reflects the research and development behind the therapeutic formulation, not simply premium ingredients.
Royal Canin Urinary SO is generally slightly more affordable per can than Hill’s c/d, though prices vary by retailer and format. Setting up a recurring order with your retailer often reduces the cost meaningfully for a food your cat will eat long-term.
At roughly 1–2 cans per day for an average adult cat, the monthly cost runs approximately:
- Hill’s c/d wet: $90–$130/month depending on format and quantity purchased
- Royal Canin Urinary SO wet: $80–$120/month
Both brands also offer dry food versions at lower cost — though wet food is strongly preferred for any cat with urinary issues due to the critical role of hydration. If cost is a concern, discuss a wet/dry combination approach with your vet rather than switching to dry-only.
Set up a recurring delivery for whichever diet your cat accepts — it removes the risk of running out, saves money on recurring orders, and means your cat never has to eat something different because you forgot to reorder. Prescription food shortages can trigger dietary inconsistency that worsen urinary conditions.
Which Cats Should Eat Which Diet
Choose Hill’s c/d Multicare if:
- Your cat has been diagnosed specifically with struvite crystals and your vet has confirmed no oxalate history
- Stress or anxiety is a contributing factor — choose the Stress variant specifically
- Your vet specifically recommended c/d based on urine culture or crystal analysis results
- Your cat has previously done well on Hill’s foods and accepts the palatability
Choose Royal Canin Urinary SO if:
- Your cat has a history of both crystal types, or the crystal type is uncertain
- Your cat has previously had calcium oxalate stones or is at risk for them
- Your cat is a fussy eater who has rejected other prescription foods
- Your vet recommended Urinary SO based on your cat’s specific urinary profile
- You want the broadest possible crystal prevention coverage in one diet
The Verdict
For the majority of cats with urinary issues — particularly those with uncertain crystal type, oxalate risk, or palatability challenges — Royal Canin Urinary SO edges ahead. The RSS technology providing validated protection against both crystal types is a meaningful clinical advantage, and the consistently higher palatability scores mean more cats will actually eat it long-term.
Exception: Hill’s c/d Multicare Stress wins for stress cystitis. If your cat’s FLUTD is linked to anxiety or stress, no other diet addresses this root cause with the same specificity. The tryptophan and casein ingredients in the Stress variant are a genuine differentiator that Royal Canin Urinary SO simply does not offer.
The honest truth is that both diets are excellent and both are significantly better for urinary health than any non-prescription food. If your vet recommended one specifically — use that one. Their recommendation is based on your cat’s individual urine test results, pH levels, and crystal type, and that information is more valuable than any general comparison guide.
If you are choosing independently or your vet said “either is fine,” Royal Canin Urinary SO is the slightly safer default for most cats. Hill’s c/d Multicare Stress is the better choice the moment stress or anxiety enters the picture.
Frequently Asked Questions
Yes, but always transition gradually over 10–14 days rather than switching abruptly. An abrupt food change can cause digestive upset in any cat, and cats with urinary issues often have sensitive systems. Mix the new food in increasing proportions over the transition period: 25% new / 75% old for 3–4 days, then 50/50, then 75% new, then 100%. Inform your vet when you switch so they can monitor whether the new diet is achieving the same urinary parameters at the next check-up. Some cats do better on one than the other and urine pH and specific gravity should be rechecked 4–6 weeks after switching.
For struvite crystal dissolution, Hill’s c/d typically achieves dissolution within 4–8 weeks of exclusive feeding. Your vet may schedule a follow-up urinalysis at 4–6 weeks to confirm crystals have dissolved. Royal Canin Urinary SO works primarily through prevention rather than dissolution — it changes the urine environment so crystals cannot form, rather than actively dissolving existing ones. For both diets, improvement in symptoms like straining and frequency can occur within 1–2 weeks as the urine becomes more dilute and pH shifts. However, exclusive adherence to the diet is essential — even occasional non-prescription food or treats can undermine the urinary effect.
For most cats with a history of urinary crystals or FLUTD, yes — long-term maintenance on a urinary diet is recommended. Urinary conditions in cats tend to recur when dietary management is stopped. The recurrence rate for struvite crystals in cats returned to a regular diet is high — studies suggest the majority of cats will redevelop crystals within 6–12 months without ongoing dietary management. Some cats with a single mild episode and no recurrence may be transitioned to a high-quality wet food diet with close monitoring, but this decision should be made with your vet based on your individual cat’s history. For cats with calcium oxalate stones requiring surgical removal, lifelong urinary diet is almost always recommended.
This article is intended for informational purposes and does not substitute for professional veterinary advice. Always consult your vet before changing your cat’s prescription diet. The comparison above reflects general formulation information — individual product formulations may vary by region and are subject to change by the manufacturer.