Most dog supplements are not well-supported by evidence. A few are. Here's an honest breakdown of what actually works, what's probably a waste of money, and the specific products worth buying in each category.
The Evidence Landscape
The supplement industry for pets is largely unregulated compared to pharmaceutical drugs. Manufacturers are not required to prove efficacy before selling. This means the supplement market includes products with strong evidence, products with weak evidence that are still reasonable to try, and products with no evidence that are pure marketing.
We've sorted the most common dog supplements by evidence quality below.
Strong Evidence: Worth Buying
Omega-3 Fish Oil (EPA/DHA)
The most evidence-backed supplement in canine nutrition. EPA and DHA omega-3 fatty acids have demonstrated benefits in peer-reviewed research for: reducing inflammation (joint disease, skin conditions, allergies), supporting cardiovascular health, improving coat quality and reducing shedding, cognitive function in aging dogs, and as adjunct therapy in kidney disease. Most commercial dog foods contain insufficient omega-3 for therapeutic benefit. Supplementing is genuinely useful for most dogs.
Dosing: EPA+DHA combined at approximately 20–55mg/kg body weight daily. For a 50 lb dog, that's roughly 500–1,250mg EPA+DHA per day. Check the label for the actual EPA+DHA content — not just "fish oil" — as concentration varies widely.
Glucosamine & Chondroitin
The evidence on glucosamine and chondroitin is moderate — human studies are mixed, but canine-specific studies are more consistently positive, particularly for dogs with existing osteoarthritis. The mechanism: glucosamine is a building block for cartilage; chondroitin inhibits enzymes that break down cartilage. Together they appear to slow cartilage degradation and reduce pain in dogs with joint disease. They are not a treatment for severe arthritis, but work well as a preventive supplement for large breeds and as a support supplement for dogs showing early joint stiffness.
Dosing: 500mg glucosamine + 400mg chondroitin per 25 lbs body weight daily. Give consistently for 4–6 weeks before evaluating effects — these work slowly.
Canine-Specific Probiotics
Evidence for probiotics in dogs is growing, particularly for: reducing acute diarrhea duration, supporting gut health during antibiotic treatment, and managing chronic digestive conditions like IBD. Purina's FortiFlora is the most well-studied canine probiotic — containing Enterococcus faecium SF68, one of the few canine-specific strains with published clinical trials. For general gut health maintenance, species-specific formulations (containing strains like Lactobacillus acidophilus, Bifidobacterium animalis, and Bacillus coagulans) are preferable to human probiotic products.
Moderate Evidence: Reasonable for Specific Situations
Coenzyme Q10 (CoQ10)
CoQ10 is an antioxidant involved in cellular energy production. In dogs, it's used most often for: heart disease support (Cavalier King Charles Spaniels and Dobermans are highest-risk breeds), cognitive dysfunction syndrome in seniors, and as a general antioxidant for aging dogs. Evidence is not robust but mechanistically plausible, and CoQ10 has an excellent safety profile. Worth discussing with your vet for dogs with cardiac conditions or cognitive decline.
CBD (Cannabidiol)
CBD for dogs is an area of active research. A Cornell University study found CBD reduced pain and increased mobility in dogs with osteoarthritis. A Colorado State University study found potential benefit in epilepsy. The evidence is preliminary but credible enough that many veterinary professionals are willing to discuss it. Key caveats: quality control varies wildly across products (look for brands with Certificate of Analysis from a third-party lab), THC content must be below 0.3% (dogs are more sensitive to THC than humans), and this is not a substitute for veterinary-prescribed pain management.
Supplements With Weak Evidence (Be Skeptical)
- Multivitamins for healthy dogs on complete-and-balanced diets: If your dog eats a nutritionally complete diet, additional vitamins typically provide no benefit and can cause toxicity if fat-soluble vitamins (A, D, E, K) accumulate.
- Antler velvet: Marketed for joint health. Evidence is insufficient to support the marketing claims.
- Colostrum supplements: Not the same as maternal colostrum. Evidence for commercial colostrum products in adult dogs is minimal.
- Most "calming" supplements (non-pharmaceutical): Chamomile, valerian, L-theanine, melatonin — some have plausible mechanisms but evidence in dogs is weak. May take the edge off mild anxiety; not effective for clinical anxiety disorders.
The Most Important Thing to Know
Supplements are not regulated the same way as drugs. A 2017 study found that many pet supplements did not contain the ingredients listed on the label at the concentrations claimed. Buy from brands that provide third-party testing certificates (Certificate of Analysis) and are transparent about their sourcing. The National Animal Supplement Council (NASC) Quality Seal indicates a brand has passed an independent audit — a useful baseline signal when evaluating unfamiliar brands.
Browse NASC-Certified Supplements →