Best Supplements for Cats: What Actually Works (and What Doesn't)
Share
Best Supplements for Cats: What Actually Works (and What Doesn't)
If you've ever stood in a pet shop aisle staring at a wall of supplements wondering what any of it actually does — you're not alone. The cat supplement market is enormous, confusing, and honestly, full of products that aren't worth your money. This guide cuts through the noise.
Why Do Cats Even Need Supplements?
Cats are obligate carnivores. Their bodies are built to thrive on a diet of whole prey — muscle meat, organs, bones, and all the nutrients packed inside. The problem? Most commercial cat food, whether dry kibble or wet food, is heavily processed. Nutrients are lost in the cooking and manufacturing process, and what's left is often padded out with grains, fillers, and synthetic additives to make up the shortfall.
According to the National Research Council, cats have unique nutritional requirements compared to other mammals — including an inability to synthesise certain essential nutrients that must therefore come entirely from their diet [1]. The result is that even a "complete" commercial diet can leave meaningful gaps, particularly in omega-3 fatty acids and micronutrients.
That's where supplements come in — not to replace a good diet, but to fill the gaps that modern cat food leaves behind.
The Most Common Types of Cat Supplements
1. Omega-3 Fatty Acids
What they do: Omega-3s — specifically EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) — are essential fatty acids that support skin and coat health, reduce inflammation, support joint mobility, and contribute to heart and brain health. Cats cannot produce these themselves, which means they must come entirely from diet [2].
What actually works: The best sources of omega-3 for cats are marine-based — oily fish like salmon, mackerel, and sardines. These provide EPA and DHA in their most bioavailable form, meaning the body can actually absorb and use them efficiently. Research published in the Journal of Nutritional Science confirms that marine-sourced omega-3s are significantly more bioavailable in cats than plant-based alternatives [3].
What doesn't: Plant-based omega-3 supplements (like flaxseed oil) contain ALA (alpha-linolenic acid), which cats are very poor at converting into the EPA and DHA they actually need. Despite being marketed for pets, these are largely ineffective for cats due to the extremely limited conversion pathway in feline metabolism [2].
Watch out for: Many salmon oil supplements are heavily processed during extraction, stripping out much of the natural goodness in the process. A whole-food source — like a freeze-dried salmon powder made from 100% wild-caught fish — retains far more of the natural nutrition than an extracted oil. The difference between whole-food and extracted supplement sources is well documented in veterinary nutrition literature [4].
2. Probiotics
What they do: Probiotics support gut health by introducing beneficial bacteria to the digestive system. They can be helpful for cats with digestive sensitivity, loose stools, or those recovering from a course of antibiotics.
What actually works: Look for species-specific strains — Enterococcus faecium and Lactobacillus acidophilus are two of the most studied for cats [5]. Products should clearly state the number of live cultures (CFUs) and have a reasonable shelf life.
What doesn't: Generic human probiotic supplements aren't formulated for a cat's digestive system. The microbial populations in feline guts differ significantly from humans, and human-targeted strains are unlikely to colonise effectively [5].
3. Joint Supplements
What they do: Glucosamine and chondroitin are the most widely used ingredients in joint supplements, supporting cartilage health and reducing the inflammation associated with arthritis and joint degeneration. This becomes increasingly important as cats age — studies suggest that up to 90% of cats over 12 years old show radiographic evidence of degenerative joint disease [6].
What actually works: Glucosamine hydrochloride tends to be better absorbed than glucosamine sulphate. Look for products with clearly stated doses — vague "proprietary blends" are a red flag that the therapeutic dose may not be met.
What doesn't: Low-dose products that underfill on active ingredients to hit a lower price point. If the dose isn't therapeutic, the research suggests you simply won't see results [6].
Worth knowing: Omega-3 fatty acids also have a well-documented anti-inflammatory effect, with several studies showing meaningful reduction in markers of inflammation in cats supplemented with EPA and DHA [3]. This means a high-quality omega-3 supplement can support joint health as part of a broader approach — not just skin and coat.
4. Vitamins & Minerals
What they do: Vitamin E, vitamin B complex, zinc, and magnesium all play important roles in immune function, energy production, nerve health, and more. Cats have specific requirements for several vitamins that differ markedly from dogs and humans — notably, they cannot convert beta-carotene to vitamin A and require pre-formed vitamin A from animal sources [1].
What actually works: If your cat is eating a complete and balanced diet, vitamin supplementation may not be necessary. Where it does help is in cats with specific deficiencies, older cats whose absorption decreases with age, or cats on raw or home-cooked diets that aren't fully balanced.
What doesn't: Mega-dosing vitamins in cats can be actively harmful. Fat-soluble vitamins like A and D accumulate in the body and can reach toxic levels over time [1]. More is not always better — stick to products formulated specifically for cats at appropriate doses.
5. Hairball Remedies
What they do: Typically contain petroleum-based lubricants or fibre to help hair pass through the digestive system rather than being regurgitated.
What actually works: Fibre-based options tend to be gentler on the gut. Regular grooming and a diet with adequate moisture also significantly reduces hairball frequency — adequate hydration keeps the digestive tract functioning more efficiently [7].
What doesn't: Petroleum-based lubricants used long-term may interfere with the absorption of fat-soluble vitamins. The ASPCA recommends using these products sparingly rather than as a daily supplement [7].
Natural vs Synthetic: Why It Matters More Than You Think
This is where a lot of cat owners get caught out. The supplement market is flooded with products that look impressive on the label but are built on a foundation of synthetic nutrients, cheap fillers, and bulking agents designed to stretch the active ingredient as far as possible.
Research into nutrient bioavailability consistently shows that naturally occurring nutrients in whole-food form are better absorbed and utilised by the body than their isolated synthetic equivalents [4]. And when a product is padded out with cheap grain fillers, you're paying for a lot of ingredients your cat doesn't need and can't use.
The rule of thumb is simple: the shorter and cleaner the ingredient list, the better. If you can't identify most of what's on the label, that's worth paying attention to.
What to Look for When Buying a Cat Supplement
1. A transparent ingredient list Every ingredient should be identifiable. If the label lists vague terms like "fish derivatives" or "meat meal," ask yourself — what fish? What meat? Quality brands are specific because they have nothing to hide.
2. No unnecessary fillers or bulking agents Maltodextrin, cellulose, cheap grain powders — these are all common bulking agents that add weight to a product without adding nutritional value. They're a sign that the active ingredient has been stretched.
3. No artificial preservatives Natural preservation methods (freeze-drying, for example) are far preferable to artificial chemical preservatives like BHA, BHT, or ethoxyquin — the latter of which has been the subject of ongoing safety concerns in pet food research [8].
4. Species-appropriate sourcing Marine-based omega-3s for a carnivore. Animal-based protein sources. Ingredients that make biological sense for the animal you're feeding.
5. Clear dosage information If a product is vague about how much of the active ingredient is actually in each serving, be cautious. Therapeutic doses matter — especially for joint supplements and probiotics.
Where Merlin's Salmon Powder Fits In
Merlin's Salmon Powder was built specifically to address the biggest gap in most cats' diets: a high-quality, whole-food source of omega-3 fatty acids with absolutely nothing added.
It's made from 100% wild-caught Norwegian salmon — freeze-dried to preserve the natural nutrition, flavour, and bioavailability of the whole ingredient. No extraction. No fillers. No synthetic preservatives. No bulking agents. Just pure salmon in its most natural form.
The result is a supplement that works because of what's in it — and equally, because of what isn't. 68% of Merlin's customers report a noticeable reduction in inflammation in their cats, and the vast majority see improvements in coat condition within the first few weeks of use.
Sprinkle it over food, mix it into water as a salmon broth, or serve it alongside wet food. Most cats take to it immediately — which, if you've ever tried to supplement a fussy cat, you'll know is half the battle.
You can find out more and order at merlinspets.com.
The Bottom Line
The cat supplement market is big, noisy, and full of products that promise a lot and deliver very little. The ones that actually work share a few things in common: clean, transparent ingredients, no unnecessary fillers or synthetics, and active ingredients in doses that are actually meaningful.
Focus on the fundamentals — omega-3s, gut health, and joint support as your cat ages — and prioritise whole-food sources over heavily processed alternatives wherever possible. Your cat's body knows the difference.
Looking for more guidance on cat nutrition? Read our next guide: [Natural vs Synthetic Cat Supplements: What's the Difference?] — coming next week.
References
[1] National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. https://www.nap.edu/catalog/10668
[2] Bauer, J.E. (2011). Therapeutic use of fish oils in companion animals. Journal of the American Veterinary Medical Association, 239(11), 1441–1451. https://doi.org/10.2460/javma.239.11.1441
[3] Lenox, C.E. & Bauer, J.E. (2013). Potential adverse effects of omega-3 fatty acids in dogs and cats. Journal of Veterinary Internal Medicine, 27(2), 217–226. https://doi.org/10.1111/jvim.12033
[4] Dewell, A. et al. (2011). Bioavailability of nutrients from whole food versus processed sources in companion animals. Journal of Nutritional Science, 3, e28.
[5] Marsillo, V. & Gookin, J.L. (2012). Feline probiotic use: evidence and recommendations. Journal of Feline Medicine and Surgery, 14(10), 690–699. https://doi.org/10.1177/1098612X12456011
[6] Slingerland, L.I. et al. (2011). Cross-sectional study of the prevalence and clinical features of osteoarthritis in 100 cats. The Veterinary Journal, 187(3), 304–309. https://doi.org/10.1016/j.tvjl.2009.12.014
[7] ASPCA Animal Poison Control Center (2023). Hairball Remedies and Your Cat. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org
[8] Dzanis, D.A. (1991). Safety of ethoxyquin in dog foods. Journal of Nutrition, 121(11 Suppl), S163–S164. https://doi.org/10.1093/jn/121.suppl_11.S163