Senior Dog Supplements: What the Evidence Supports

Supplements are the least regulated part of dog care and the most heavily marketed to owners of aging dogs. A short list has evidence. The rest ranges from harmless to harmful.

Strong to moderate evidence

Omega-3 fatty acids (EPA and DHA from fish oil). The best-supported supplement for seniors. Reduces lameness scores and NSAID needs in arthritis in multiple controlled trials; supportive evidence in heart disease, kidney disease and cognitive decline. Therapeutic doses are high (your vet will set them by body weight); flaxseed oil does not convert efficiently in dogs. Choose a product with third-party purity testing.

Diets and supplements for cognitive decline. Antioxidant-enriched diets and medium-chain triglycerides improved memory and learning in controlled trials of older dogs. SAMe has modest evidence.

Probiotics, for specific uses. Trial evidence for shortening diarrhea and for support during antibiotics, with strain-specific products. Not shown to help healthy dogs.

Weak or inconsistent evidence

Glucosamine and chondroitin. Widely used; controlled trials show little or no effect over placebo, and product content varies enormously. Unlikely to harm.

Green-lipped mussel, turmeric or curcumin, MSM, boswellia, CBD. Small trials with mixed results. Generally tolerated. CBD affects liver enzymes and drug metabolism.

Joint injections (polysulfated glycosaminoglycan). A prescription product, moderate evidence, a legitimate part of an arthritis plan.

Avoid or use only with a vet

• Vitamin D, calcium, iron: easy to overdose, dangerous in excess
• Human supplements containing xylitol (some gummies and chewables): toxic to dogs
• Garlic and onion products: damage red blood cells
• High-dose vitamin A: liver and bone toxicity
• “Immune boosters”, “detox” and “anti-cancer” blends: no evidence, and a delay to real treatment

How to decide

Start from a diagnosis, not a symptom. Arthritis: fish oil plus proven pain relief. Cognitive signs: a brain-support diet and possibly selegiline. Kidney disease: a kidney diet, and fish oil if your vet agrees. Healthy senior: a complete diet, ideal weight, dental care, exercise. Bring every supplement bottle to the six-monthly check-up so the vet can check for interactions with medication, which is where most supplement harm in seniors actually comes from.