Does fish oil actually work for dogs and cats?

If your pet has stiff joints, start here

Most supplement claims rest on a mechanism and a hopeful testimonial. Fish oil for joints rests on actual outcomes, which is rare in this aisle. A 2022 systematic review and meta-analysis of nutraceuticals for canine and feline osteoarthritis found that omega-3 fatty acids produced a clear clinical analgesic effect, the strongest result of any joint active reviewed (Barbeau-Gregoire 2022, PMC9499673). Underneath that review sit randomized controlled trials like Roush 2010, in which dogs with osteoarthritis fed an omega-3-rich diet showed measurable improvement in how they bore weight on the affected limb (Roush 2010, PMID 20043800). In plain terms: dogs in pain moved better.

That is a higher bar than the aisle usually clears. To be clear about what this is not: omega-3 is not a cure for arthritis, and it is not a substitute for the pain management your vet can offer. But easing the pain of a degenerative joint disease with a food-derived supplement is a genuine, repeatable finding, and that is why our rubric ranks omega-3 products at the top of the evidence ladder.

If you are after a better coat, the case is real but quieter

The other big reason people buy fish oil is for itchy skin and a dull coat, and here the evidence is solid but more modest, so set your expectations accordingly. If you have an itchy dog, randomized trials show that essential-fatty-acid and omega-3 supplementation improves atopic dermatitis scores and can reduce the dose of conventional medication needed to control the itch (Glos 2008, PMID 18477332; a 2024 dose-sparing trial, PMID 38465482). For cats, a 2025 double-blinded trial found that an EPA and DHA-elevated diet roughly halved the medication a cat needed for atopic skin disease (Watson 2025, PMID 40427306), though a 2021 systematic review grades the feline evidence as low-to-moderate (Mueller 2021, PMID 33470011). So it can help, but lean on your vet rather than expecting fish oil to do the whole job.

One honest caveat is worth knowing before you buy: the strongest skin trials delivered omega-3 as part of a complete therapeutic diet, not as a standalone oil squirted on top of dinner. That does not erase the benefit. It does mean that a label promising a glossy coat from a few pumps is reaching past what the research actually tested.

How to tell a good bottle from a useless one

Here is where you do the work that actually matters. Because the ingredient itself is so well evidenced, the only real question is whether a given bottle delivers enough of it. The two fatty acids that matter are EPA and DHA, and the big "fish oil" number on the front of the bottle is not the same thing. A supplement can shout "1,200 mg fish oil" and still hand over only a few hundred milligrams of actual EPA and DHA, well under what the trials used for a mid-size dog. So flip the bottle over and find those two numbers.

This is exactly what our Active Dose sub-score checks for you. It is why two fish-oil products with the same well-evidenced ingredient can score differently: the one that discloses and delivers a studied EPA and DHA dose earns it, and the one that hides behind a blend or under-doses does not. It is also why we are comfortable putting omega-3 at the top of the evidence-backed supplements list while still scoring individual bottles on their own merits.

Before you start, a few honest limits

Good evidence for an ingredient is not a green light to wing it. Omega-3 can interact with other conditions and medications, the right dose depends on your particular animal, and more is not better past a point. So the takeaway is narrower, and more useful, than the marketing: if you are going to spend on one supplement for an arthritic dog or cat, the evidence points at fish oil first, and your veterinarian can help you land on the right dose.

- The PetScored desk. See how we tier evidence in the supplements methodology, and the omega-3 products we score under skin and coat supplements.