Key Takeaway: Veterinary consensus supports routine use of only a handful of supplements—omega-3 fatty acids, joint nutraceuticals (glucosamine HCl, chondroitin sulfate, avocado/soybean unsaponifiables, green-lipped mussel), and probiotics—due to robust clinical and mechanistic evidence. Other popular ingredients lack the rigorous trials needed for veterinary endorsement. 1. Omega-3 Fatty Acids Active Ingredients: Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) Mechanisms and Benefits: Evidence Grade: 2. Joint Nutraceuticals Evidence-Based Ingredients: Mechanisms and Benefits: Veterinary Evidence: 3. Probiotics Active Ingredients: Multi-strain bacterial blends (e.g., Lactobacillus, Bifidobacterium species) Mechanisms and Benefits: Evidence Level: 4. Supplements Without Routine Veterinary Endorsement Despite heavy marketing, the following lack sufficient high-quality evidence for routine recommendation: 5. Practical Veterinary Recommendations Conclusion Veterinarians recommend supplements only when backed by well-designed trials and clear mechanisms. Omega-3s, select joint nutraceuticals, and probiotics meet this standard. All other ingredients require further research before routine veterinary endorsement.