Fish Oil for Dogs: What the Research Found

Trials in dogs with osteoarthritis point toward improvement with omega-3 fatty acids from fish oil, and a 2012 review rated omega-3 in dogs the only nutraceutical it examined with more than low-strength evidence. The trials are small and short, several have company ties, and one placebo-controlled fish oil trial found no significant difference on its main outcomes.

What did the reviews conclude?

Two systematic reviews that included dogs singled out omega-3 fatty acids among the nutraceuticals for osteoarthritis. Fish oil supplies mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Lenox and Bauer, 2013, Journal of Veterinary Internal Medicine).

The 2012 review covered 22 papers across horses, dogs and cats and rated the evidence low for every nutraceutical except omega-3 fatty acids in dogs. It noted that rigorous randomized trials and participant numbers were limited (Vandeweerd et al., 2012, Journal of Veterinary Internal Medicine). A 2022 meta-analysis of 72 trials in dogs and cats reported evident clinical analgesic efficacy for omega-3-enriched diets and supplements (Barbeau-Grégoire et al., 2022, International Journal of Molecular Sciences).

What do the osteoarthritis food trials show?

Food trials mostly reported improvement, with owner reports carrying much of the result. In a randomized, double-blind trial of 127 dogs at 18 clinics, dogs fed an omega-3-enriched food for 6 months had higher blood omega-3 levels than dogs on a typical commercial food, and owners reported a better ability to rise, play and walk (Roush et al., 2010, Journal of the American Veterinary Medical Association). The abstract doesn't name a funder, and the test food also differed in omega-6 to omega-3 balance, so it tested a diet rather than one ingredient.

A second trial of 38 dogs added force-plate analysis, which records how much weight a dog puts through a limb. Over 90 days, peak vertical force rose 5.6% on the fish-oil-enriched food and 0.4% on control food, and improved in 82% of test-food dogs against 38% of controls (Roush et al., 2010, Journal of the American Veterinary Medical Association). That outcome was measured, not rated. But 38 dogs is a small trial.

A 131-dog trial at 33 hospitals tracked how much carprofen, a prescription pain drug, dogs needed. The need fell faster on the supplemented food, as judged by investigators and owners (Fritsch et al., 2010, Journal of the American Veterinary Medical Association). Its first author lists Hill's Pet Nutrition, a pet food company, as an affiliation. The endpoint was a drug requirement set by judgment, not a measured change in the joint.

In 30 dogs over 13 weeks, force-plate peak vertical force rose by 3.5% of body weight on a fish-derived omega-3-rich veterinary diet and by 0.5% on control food, a difference that was not statistically significant. Owner-scored everyday activities improved only in the diet group (Moreau et al., 2013, Journal of Animal Physiology and Animal Nutrition).

What do the fish oil supplement trials show?

Two placebo-controlled supplement trials reached different conclusions. In 77 dogs, a deep sea fish oil product was compared with corn oil for 16 weeks. Groups did not differ significantly on force-plate measures, a validated chronic pain index or rescue pain medication use. The fish oil group improved against its own baseline, and its owners were more satisfied and better at guessing their dog's group (Hielm-Björkman et al., 2012, BMC Veterinary Research). The authors call the study un-commissioned. A report by the same group found that corn oil also shifted some blood markers and seems not to be a good placebo, which makes the null result harder to read (Barrouin-Melo et al., 2016, Lipids in Health and Disease).

In 78 dogs, an EPA and DHA oil scored better than a placebo oil on discomfort, lameness and joint severity at day 84, with no major side effects reported (Mehler et al., 2016, Prostaglandins, Leukotrienes and Essential Fatty Acids). The first author lists a commercial affiliation, and another author lists OmegaQuant Analytics.

Foods and supplements are different interventions, so what holds for one doesn't carry over to the other.

What about skin and coat?

The two most recent trials in dogs with atopic dermatitis report lower itch scores and lower drug needs, but the clinician-scored lesion index did not differ between groups. An older placebo-controlled trial of 29 dogs found clinical scores improved over 10 weeks with flax oil or a commercial EPA and DHA preparation, but not with mineral oil (Mueller et al., 2004, Journal of Small Animal Practice).

In 36 dogs on cyclosporine, a mainly omega-3 product over 12 weeks allowed a larger cyclosporine reduction than placebo and improved owner-scored itch more, with no significant difference in the clinician-scored lesion index. The abstract does not name the oil source, and two authors list Novartis Animal Health as an affiliation (Müller et al., 2016, Veterinary Journal).

In 22 dogs already receiving oclacitinib, a fish oil product for 16 weeks, against paraffin oil, allowed a significant drug reduction that the placebo group did not show, and a lower itch score at day 112. The lesion index did not change over time or differ between groups, and no adverse events were observed (Schäfer and Thom, 2024, Veterinary Dermatology).

Does the quality of the oil matter?

A 2025 analysis found canine fish oil supplements varied widely in EPA and DHA content, with some missing their label claims. Across eleven supplements from two time points, 2010 and 2021, there were six instances of a product not meeting its label claim within 5% for EPA, DHA or both. Mercury, lead, cadmium and PCBs were not detected (Ober et al., 2025, Topics in Companion Animal Medicine). The abstract reports no rancidity measure or dog outcome, and samples from 2010 and 2021 cannot grade anything sold now.

What the research did not show

The trials do not show what fish oil does in dogs without these conditions, over the long term, or to the joint itself. They enrolled dogs that already had osteoarthritis or atopic dermatitis, and their outcomes were owner or investigator scores, force-plate readings, blood measures and drug-dose requirements. The abstracts report no imaging or tissue measure of whether the joint itself changed. The longest ran 6 months, and none compared a food with a supplement head to head.

Where your veterinarian fits in

Whether fish oil makes sense depends on your dog's weight, medications and conditions, which is a conversation for your veterinarian. A review of potential adverse effects in dogs and cats lists altered platelet function, gastrointestinal effects, effects on wound repair, weight gain and nutrient-drug interactions among its concerns (Lenox and Bauer, 2013, Journal of Veterinary Internal Medicine). Your vet should know about any fish oil your dog gets, especially before a procedure and alongside any prescription medication.

Bring the product label, a list of current medications, and a dated note of what you see at home, such as how your dog gets up after rest. Ask the company for its testing paperwork too, since the audit above found labels did not always match contents.

Where to go from here

Our reading of the joint supplement research is in senior dog joint care. We applied the same question to another popular supplement in do probiotics work for dogs?. Pair a solid foundation with peptides: explore BPC-157, TB-500 and GHK-Cu.