Supplements: what the evidence says

A complete-and-balanced food already meets nutritional requirements. Supplements are for specific situations, not general insurance. If your dog is healthy and eating a complete diet, the honest answer for most of this aisle is that you do not need it.

Where they sit: Pet supplements are neither drugs nor food. They fall in a gap overseen loosely by the FDA's Center for Veterinary Medicine and by individual state feed-control officials.

What that means in practice: There is no pre-market approval and no requirement to prove a product does anything. A company can put an ingredient on a shelf without a single trial behind the claim on the front.

The nasc seal: The National Animal Supplement Council seal is the strongest quality signal available. It means the company submitted to manufacturing audits and reports adverse events. It does NOT mean the product works — it is a quality signal, not an efficacy one, and that distinction is worth holding onto.

Third party testing: Look for a company that publishes certificates of analysis. If they will not tell you what is actually in the bottle, that is the answer.

Strong means multiple controlled trials point the same way. Moderate means real evidence with real limits. Weak means the trials exist and are unconvincing. None means the marketing is ahead of the science. This is about the INGREDIENT, not the brand.

Grade: STRONGEST EVIDENCE of anything in this section

What the research found: A 2022 systematic review and meta-analysis screened 1,578 publications and included 57 articles covering 72 trials across nine categories of natural health product. Omega-3-enriched diets and omega-3 supplements showed clear clinical analgesic efficacy in dogs with osteoarthritis. Of everything tested, this is the ingredient that held up.

What it helps: Joint pain and mobility, skin and coat, with additional evidence around kidney and cognitive support.

The number that matters: EPA and DHA content in milligrams. That is the only figure worth comparing between products — 'fish oil' on a label tells you nothing about dose, and most products are underdosed.

Practical: Ask your vet for an amount rather than guessing; it is easy to overdo. Store it cold, because rancid oil is worse than none. Give it four to eight weeks before judging it.

The interaction to mention: Omega-3s and NSAIDs both act on the eicosanoid pathway, and omega-3s affect clotting. Combining them is a clinical decision, so tell your vet what you are giving.

Grade: Glucosamine and chondroitin: WEAK. Green-lipped mussel and UC-II collagen: MODERATE.

The finding: Glucosamine and chondroitin are the most-sold joint supplements and among the least supported. In recent reviews they did not produce a meaningful effect on pain or mobility, and in some trials the control dogs receiving nothing did as well or better. A placebo-controlled trial comparing glucosamine/chondroitin against marine fatty acid compounds and an NSAID found the marine compounds and the NSAID produced significant improvement in measured limb loading while glucosamine did not.

Why it is still everywhere: It has been recommended for decades, it is safe, and it is cheap to manufacture. Habit and harmlessness keep a product on the shelf for a long time after the evidence stops supporting it.

Green-lipped mussel: Perna canaliculus. Multiple studies verify a benefit in arthritic dogs, and Cornell notes roughly 77 mg per kilogram of body weight per day is needed to see it. Check the dose against your dog's weight, because many products fall short.

UC-II collagen: Undenatured type II collagen has produced better trial results than glucosamine, and appears to work best given separately from other joint ingredients rather than in a combined blend.

What actually helps most: Weight control. The American College of Veterinary Surgeons puts it at the top of arthritis care, ahead of every supplement, and it costs nothing. Every extra pound loads every joint at every step. After that: low-impact exercise, traction on slick floors, a ramp instead of a jump, and prescription pain relief when your vet says it is time.

Grade: MODERATE, and specific — strong for one situation, thinner for the rest

The best-supported use: Acute diarrhea. One controlled trial found probiotics resolved it in about 3.5 days versus 4.8 days for placebo — comparable to metronidazole. A systematic review of 17 controlled trials found 14 reported positive gastrointestinal outcomes.

The part marketing leaves out: The evidence is for SPECIFIC STRAINS at specific doses, not for anything labeled 'probiotic'. Enterococcus faecium SF68, Bifidobacterium longum BL999 and Bifidobacterium animalis AHC7 are among the best studied in dogs. A different product with different strains is not the same product.

The honest caveat: A 2025 analysis found only about half of canine and feline probiotic trial abstracts were later published as full papers, which suggests negative results may be underreported. That does not invalidate the positive findings, but it should temper confidence in the broader claims.

What to check on the label: Strains named individually, colony-forming units guaranteed THROUGH EXPIRY rather than at manufacture, and the NASC seal. Human yoghurt is not a substitute.

When it is worth it: Antibiotic courses, stress or travel diarrhea, and diet transitions. Less clearly useful as a daily supplement in a healthy dog.

Grade: MODERATE for arthritis pain, and legally messy

What the research found: The same 2022 meta-analysis found cannabidiol showed clinical analgesic efficacy, though to a lesser degree than omega-3s. A separate systematic review pooled five studies covering 117 dogs with osteoarthritis.

The safety signal to know: A Cornell study reported improvements in comfort and activity but also elevations in alkaline phosphatase, a liver enzyme. That is a reason for bloodwork if you use it long term, not a reason to panic.

The practical problems: Product quality varies enormously, dosing in dogs is not well established, and the legal position differs by state. Veterinarians in some states are restricted in what they can say about it.

If you use it: Choose a product with a published certificate of analysis, start low, and tell your vet so liver values can be watched.

Grade: WEAK to MODERATE, and situational

The honest version: L-theanine, alpha-casozepine and pheromone products show modest effects at best. They are worth trying for mild, predictable stress — a car journey, a storm — and are not a substitute for a behavior plan.

The thing worth saying: If your dog has genuine separation distress or noise phobia, veterinary medication is not a failure and not a last resort. Anxiety is a welfare problem, and leaving a dog in it while working through supplements is a long time to be frightened.

Grade: NO EVIDENCE OF BENEFIT in a dog on a complete diet

Why: A complete-and-balanced commercial food already contains what a multivitamin provides. Adding one is topping up what is already there, and fat-soluble vitamins can accumulate to harmful levels.

When they do make sense: Homemade diets — which should be formulated by a veterinary nutritionist anyway — and specific deficiencies your vet has identified.

MSM, turmeric and curcumin, hyaluronic acid given by mouth, apple cider vinegar, colloidal silver, and most 'immune support' blends. Some may turn out to help. Right now the canine trials either do not exist or are not convincing, and dosing is largely scaled down from human products with no canine basis.

· A named ingredient WITH a dose, not a proprietary blend that hides the amounts
· For fish oil: EPA and DHA in milligrams, not total oil
· For probiotics: strains named individually, CFUs guaranteed through expiry
· The NASC quality seal
· A published certificate of analysis
· No cure claims. Nothing in this aisle cures anything, and a product saying otherwise is telling you what kind of company it is

· Does my dog actually need this, given what they eat?
· What dose, for this weight?
· Does it interact with anything they are already on?
· How long before we would know whether it is working?
· Is there something with better evidence for the same problem?

If you buy one thing for an arthritic dog, make it omega-3s at a proper dose — and keep them lean, which matters more than anything you can buy. If you buy one thing for a dog on antibiotics, make it a strain-specific probiotic. For a healthy dog on a complete diet, the honest answer is usually nothing at all. We would rather say that than sell you a subscription.