Of the omega-3 fats, the two that matter for dogs are EPA and DHA. They are best studied in dogs with osteoarthritis, and in a 2022 review of 72 trials, omega-3 eased pain more clearly than any other type of product. For skin, kidneys, heart and brain there are promising studies, but they are small, and we found no study in dogs on sleep.
EPA, DHA and where they come from
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are long-chain omega-3 fatty acids. They form part of cell membranes, and DHA is plentiful in the brain and the retina. Plants provide a different omega-3, ALA (linseed, chia), which does not do the same job: in the boxer study further down, linseed oil had no effect and fish oil did.
There are three main sources on the market:
- Fish oil (anchovy, sardine, salmon and others). Almost every trial in dogs has used it.
- Krill oil, from a small Antarctic crustacean. It provides EPA and DHA, but has fewer studies in dogs.
- Algal oil. The EPA and DHA in the sea is made mostly by microalgae and reaches fish through what they eat. These algae are now grown in tanks and their oil is extracted. How much EPA and how much DHA it contains varies from one oil to another, so read the label.
Algal oil with EPA and DHA has safety data in dogs. In a study of beagle bitches and their puppies, an algal oil with about 50% EPA plus DHA (the batch used had roughly 400 mg of DHA and 125 mg of EPA per gram, more than three times as much DHA as EPA) was added to the food (up to 3% of dry weight) from mating, through pregnancy and lactation, and in the puppies until 26 weeks after weaning. It was well tolerated, blood tests and clotting did not change, and blood EPA and DHA rose in both generations.
Green-lipped mussel is another marine source of omega-3, with other compounds as well. It has its own page.
What research in dogs has found
Joints and osteoarthritis
Joints have the most studies, and the best-quality ones, among them a 2022 systematic review with meta-analysis that pooled 72 trials of enriched diets and products for dogs and cats with osteoarthritis. The two omega-3 groups (therapeutic diets, and products with fish oil or green-lipped mussel) showed the clearest effect on pain, and were among the groups with the most good-quality trials. Only one in ten omega-3 trials found no effect at all. In the same review, glucosamine and chondroitin products showed no effect.
The review's authors add that many of these studies lack objective measures, and that in diet trials more dogs in the control group improve than in drug trials. The treatments lasted between one and six months.
Skin and atopic dermatitis
A trial of 36 atopic dogs already on ciclosporin gives more modest evidence for the skin. One group received a mainly omega-3 product for 12 weeks and the other a placebo. In the omega-3 group the drug could be cut back further (the median dose went from 4.1 to 2.6 mg/kg a day, against 3.5 to 3.3 mg/kg on placebo) and itching improved more. The vet's scores for skin lesions, on the other hand, moved by a similar amount in both groups. Omega-3 was added to ciclosporin here and allowed its dose to come down; it was not tested as a replacement for the drug.
Kidneys
The most direct study of omega-3 and kidney failure, published in 1998, was done in 21 laboratory dogs that had most of their kidney tissue removed surgically. They were split into three groups that ate the same diet with 15% added fat for 20 months: fish oil, safflower oil (rich in omega-6) or beef tallow. The fish oil group had less protein in the urine, lower creatinine and cholesterol, and less damage to the kidney tissue. The omega-6 group did worst, with the lowest filtration.
That is a surgical model with seven dogs per group, and we have not found trials testing omega-3 on its own in dogs with naturally occurring kidney disease. If your dog has kidney disease, talk to the vet before adding anything to its diet.
Heart
In 24 boxers with arrhythmogenic cardiomyopathy, dogs with more than 95 ventricular premature beats a day were given 2 g of fish oil, linseed oil or sunflower oil daily for six weeks. Only fish oil brought the premature beats down (the median fell from 397 to 162 in 24 hours). Linseed oil, which supplies plant ALA, made no difference. It is a small, short study that measured arrhythmias, not survival.
Brain and retina in puppies
A study fed 48 beagle puppies a food low, moderate or high in DHA from fish oil between 8 and 52 weeks of age. The high-DHA puppies did better at a reversal learning task (unlearning the correct response and learning the opposite one). They also told visual contrasts apart better, moved more easily through an obstacle maze in the first tests and had more antibodies in the two weeks after their rabies vaccination. The more DHA they had in their blood, the stronger the retina's response on the electroretinogram. But the high-DHA food also contained more vitamin E, taurine, choline and L-carnitine, so not all of the effect can be put down to DHA.
Older dogs and cognition
A 2025 systematic review gathered 30 studies, almost all in dogs, on diets and products for cognitive function in older animals. Omega-3s showed benefits, especially at high doses. Vitamins E and C on their own did less well, although the authors point out that they are needed to stop omega-3 from oxidising. They also call for studies with more consistent protocols, better control groups and objective tests as well as questionnaires.
Sleep and hormones
Many people link omega-3 with better sleep or with balancing hormones. There is no dog study on sleep to cite, for or against, and none showing changes in the thyroid, cortisol or sex hormones.
Eicosanoids (prostaglandins, thromboxanes, leukotrienes and others) are signalling molecules that act as local hormones in inflammation, blood clotting and the immune response. They are made mainly from an omega-6, arachidonic acid, and EPA and DHA compete with it for the same enzymes. When the diet carries more omega-3, that production shifts. In beagle bitches aged 9.5 to 11.5 years fed an omega-6:omega-3 ratio of 1.4:1 for 8 to 12 weeks, stimulated immune cells produced 52% less prostaglandin E2 than on a ratio of 31:1. This is the route by which omega-3 is thought to act on inflammation.
Doses used in studies
There is no single dose, and in osteoarthritis the 2022 review did not find that the dose changed the result, although within each type of product the doses were fairly similar. These are amounts used in the studies cited here:
- Boxers with arrhythmias: 2 g of fish oil a day for six weeks.
- Pregnant bitches and puppies: algal oil up to 3% of the dry food.
- Healthy huskies: 0.45 and 0.71 g of EPA+DHA per kg of metabolic body weight a day for eight weeks (see below).
In 2006 the NRC (the US National Research Council) set a safe upper limit of EPA+DHA for adult dogs of 0.37 g per kg of metabolic body weight (weight in kg raised to the power 0.75) a day. A 2026 study of 27 huskies (25 Siberian and 2 Alaskan) notes that this figure rested mainly on a single study, the one in older beagles cited above. It tested 0.03, 0.45 and 0.71 g per kg of metabolic weight for eight weeks. The two higher amounts, both above the NRC limit, were well tolerated and did not raise markers of oxidation or inflammation. At eight weeks, though, blood vitamin E was lower in the highest group (3.52 against 5.82 µg/ml in the low group). The authors note that the study food was high in vitamin E, which may have damped down oxidation.
Worked out from the NRC figure (0.37 multiplied by body weight to the power 0.75), the limit looks like this:
| Dog's weight | NRC safe upper limit (EPA+DHA a day) |
|---|---|
| 5 kg | 1.2 g |
| 10 kg | 2.1 g |
| 20 kg | 3.5 g |
| 30 kg | 4.7 g |
| 40 kg | 5.9 g |
These are grams of EPA and DHA, not grams of oil. Check the label, which should state how much EPA and DHA each serving provides. For your own dog's dose, particularly if it is unwell or on medication, ask the vet.
Side effects, from loose stools to bleeding
A review of the adverse effects of omega-3 in dogs and cats covers the ones to keep in mind:
- It can upset the digestion. If you notice soft stools or diarrhoea, lower the amount and build it back up slowly.
- Omega-3 can alter how platelets work, and the review also mentions effects on wound healing. Ask first if your dog has a clotting disorder, takes anticoagulants or is due for surgery.
- Omega-3 fats oxidise easily and raise the need for vitamin E. In the older beagles, blood vitamin E was 20% lower and fat oxidation higher on the 1.4:1 diet than on the 31:1 diet. In the high-dose huskies, vitamin E also ended up lower. An oil that has gone rancid and smells strong is best thrown away.
- In the same beagles, the diet richer in omega-3 reduced an immune response in the skin (the delayed-type hypersensitivity test). What that means in everyday life is not known, but it is a reason not to overdo it.
- If your dog is diabetic, discuss it with the vet: the review mentions possible effects on glucose control and insulin sensitivity.
- Oil is fat and adds calories. A poorly purified oil can carry contaminants, and some oils, such as cod liver oil, also supply vitamins A and D.
Bleeding gums, bruising, or persistent diarrhoea or vomiting mean it is time to stop the omega-3 and phone the vet.
Sources
- Safety of a novel feed ingredient, Algal Oil containing EPA and DHA, in a gestation-lactation-growth feeding study in Beagle dogs. PLoS One, 2019.
- A 2022 Systematic Review and Meta-Analysis of Enriched Therapeutic Diets and Nutraceuticals in Canine and Feline Osteoarthritis. International Journal of Molecular Sciences, 2022.
- Evaluation of cyclosporine-sparing effects of polyunsaturated fatty acids in the treatment of canine atopic dermatitis. The Veterinary Journal, 2016.
- Beneficial effects of chronic administration of dietary omega-3 polyunsaturated fatty acids in dogs with renal insufficiency. Journal of Laboratory and Clinical Medicine, 1998.
- Omega-3 fatty acids in Boxer dogs with arrhythmogenic right ventricular cardiomyopathy. Journal of Veterinary Internal Medicine, 2007.
- Evaluation of cognitive learning, memory, psychomotor, immunologic, and retinal functions in healthy puppies fed foods fortified with docosahexaenoic acid-rich fish oil from 8 to 52 weeks of age. Journal of the American Veterinary Medical Association, 2012.
- Enhancing cognitive functions in aged dogs and cats: a systematic review of enriched diets and nutraceuticals. GeroScience, 2025.
- The ratio of dietary (n-6) to (n-3) fatty acids influences immune system function, eicosanoid metabolism, lipid peroxidation and vitamin E status in aged dogs. Journal of Nutrition, 1997.
- Revisiting eicosapentaenoic acid and docosahexaenoic acid recommendations for healthy Siberian Huskies at maintenance: greater dietary EPA and DHA increase plasma lipid incorporation and reduce α-tocopherol concentrations. Journal of Animal Science, 2026.
- Potential adverse effects of omega-3 fatty acids in dogs and cats. Journal of Veterinary Internal Medicine, 2013.