The pet supplement market has grown to billions of dollars annually — and is regulated with significantly less rigor than human pharmaceuticals or even human dietary supplements. Unlike prescription veterinary medications, most pet supplements don’t require proof of efficacy before being sold, don’t undergo standardized manufacturing quality controls, and can make health claims that aren’t required to be substantiated by clinical evidence.
This doesn’t mean all pet supplements are useless — several have legitimate evidence supporting specific benefits. It means that navigating the market requires knowing which ones actually work, which are oversold, and which are a waste of money at best or potentially harmful at worst.
The Regulatory Gap
In the United States, pet supplements are primarily regulated under the National Animal Supplement Council (NASC) guidelines and some state feed laws — not by the FDA as drugs. This means manufacturers are not required to demonstrate efficacy before marketing a supplement, manufacturing quality varies enormously, label claims are poorly verified, and active ingredient concentrations may not match label claims.
When choosing supplements, look for NASC certification (indicates quality manufacturing standards), third-party testing verification, and prefer supplements where your veterinarian can recommend a specific, tested product.
The Supplements With Genuine Evidence
Omega-3 Fatty Acids (Fish Oil)
The best-evidenced supplement for both dogs and cats. EPA and DHA from marine sources (fish oil, algae-based EPA/DHA) have documented benefits including: reduced inflammation throughout the body, improved skin and coat quality, support for cardiovascular health, reduction of joint inflammation in arthritis, potential cognitive benefits in aging animals, and anti-cancer effects in some contexts.
The evidence: multiple published clinical trials in dogs and cats. This is not a supplement category where you’re operating on hope — the research is solid.
Dosing: typically 20–55mg EPA+DHA per kilogram of body weight daily for anti-inflammatory effects. Your veterinarian can advise specific dosing for your pet’s weight and health status.
Important note: fish oil oxidizes and becomes rancid relatively quickly. Store refrigerated after opening and replace within 60–90 days. Rancid fish oil is not just ineffective — it’s potentially harmful. Consider capsules rather than liquid for easier quality control.
Probiotics
Growing evidence supports probiotic use in pets, particularly for: gastrointestinal conditions (diarrhea, inflammatory bowel disease), immune support, skin conditions with an allergic component, and recovery from antibiotic courses (which disrupt the microbiome significantly).
The challenge: not all probiotics are created equal. Species specificity matters — probiotic bacteria that benefit humans or dogs may not colonize or benefit cats effectively. The research supports species-specific products: Fortiflora (Purina) for both dogs and cats has the most published research of any pet probiotic. Proviable (Nutramax) is another well-researched option.
Check that the product: lists the specific bacterial species and CFU count, guarantees viability at the time of use (not just manufacture), and comes from a reputable manufacturer.
Glucosamine and Chondroitin
Perhaps the most commonly recommended joint supplement for dogs — and the one with the most mixed evidence. The theory is sound: glucosamine is a precursor to glycosaminoglycans, structural components of cartilage; chondroitin inhibits cartilage-degrading enzymes. The clinical evidence for meaningful benefit in dogs is weaker than once believed, with some well-designed studies showing benefit and others showing little effect.
The practical assessment: available evidence suggests modest benefit at best — not the dramatic arthritic improvement sometimes claimed. Some dogs do appear to respond meaningfully. Given a reasonable safety profile at appropriate doses, many veterinarians recommend a trial period (4–8 weeks) to assess individual response. If no improvement is observed, it’s unlikely to be helping.
Cosequin DS and Dasuquin (Nutramax) are the most studied commercial products and represent more reliable options than many generics.
Turmeric and Curcumin
Curcumin has documented anti-inflammatory mechanisms, and some veterinarians have advocated for its use in arthritic pets. The challenge is the same as in humans: curcumin has extremely poor bioavailability in standard formulations, and while there is mechanistic evidence for anti-inflammatory effects, clinical trials in dogs and cats are limited.
Some formulations improve bioavailability through piperine or lipid-based delivery systems. If using turmeric for a pet, a standardized curcumin product with enhanced bioavailability is necessary for any potential benefit — plain culinary turmeric at the doses used in food provides negligible amounts.
Coconut Oil
Heavily marketed for pets as beneficial for skin, coat, and digestion. The evidence for meaningful health benefits is weak, and the high saturated fat content raises the same concerns as in humans. Some pets appear to enjoy it as a food topper, but as a therapeutic supplement, the evidence doesn’t support the marketing.
The Supplements With Insufficient Evidence
CBD/Hemp oil: A rapidly growing market with very limited published research in pets. Some preliminary evidence suggests possible benefit for anxiety and pain in dogs, but dose-finding, safety, and efficacy data are insufficient to make confident recommendations. Discuss with your veterinarian before use — product quality varies enormously and some products contain higher THC levels than labeled.
Milk thistle: Traditionally used for liver support. Some evidence in humans, very limited in dogs and cats. May be worth discussing with your veterinarian for pets with known liver disease — not for routine supplementation.
Collagen supplements: The same concern as in humans — dietary collagen is digested into amino acids and does not specifically end up in joints or skin. No compelling evidence for meaningful benefit in pets.
When to Supplement vs. When to Treat
Supplements are not treatments. A pet with diagnosed arthritis, kidney disease, inflammatory bowel disease, or any other medical condition should be receiving veterinary-recommended treatment — supplementation may be a useful adjunct but never a substitute for appropriate veterinary care.
Always discuss supplements with your veterinarian before beginning them — some supplements interact with medications or are contraindicated in certain health conditions. For example, fish oil at high doses has anticoagulant effects that matter before surgery.
→ Read Next: What to Feed Your Dog — A Complete Guide to Canine NutritionThe Bottom Line
The supplement landscape for pets is full of products ranging from genuinely evidence-backed to largely unsubstantiated. Omega-3 fatty acids (fish oil) are the clear standout — well-evidenced across multiple health outcomes in dogs and cats. Probiotics from species-specific, well-researched products have legitimate evidence for specific conditions. Glucosamine-chondroitin may provide modest benefit for some arthritic dogs and is worth a trial. Beyond these, apply healthy skepticism and consult your veterinarian before adding any supplement to your pet’s regimen.
Emma Hartwell is a lifelong animal lover, certified pet nutritionist, and experienced dog trainer with over 8 years of hands-on experience working with animals of all kinds. She founded InnerzNews to give pet owners access to honest, practical, and science-backed advice — because every animal deserves the best possible care. When she’s not writing, Emma is hiking with her two rescue dogs, Milo and Biscuit, or volunteering at her local animal shelter.