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fish oil for dogs

September 22, 2026

Fish Oil for Dogs: Benefits, Dosage and Side Effects

Fish oil for dogs: where omega-3 (EPA and DHA) helps most, from arthritis to itchy skin, how much to give by weight, how to choose one and side effects.

Written and reviewed by , CEO

An older dog stands beside a food bowl and a separate spoon of golden oil.

omega 3 good for dogs

TL;DR

Fish oil for dogs is one of the best-studied supplements there is, and the omega-3 it supplies (EPA and DHA) is good for many dogs, but how good depends on the problem. The strongest evidence is for arthritis: in several controlled trials, dogs fed extra fish-oil omega-3 (EPA and DHA) moved better or needed less pain medication, and systematic reviews rank omega-3 above every other joint supplement. There is supporting evidence for itchy, allergic skin, and smaller studies on brain development and heart disease. For a healthy dog already eating a complete and balanced food, a supplement is optional. What counts on a label is the amount of EPA plus DHA, not the total amount of oil.

What omega-3 is

Omega-3s are a family of fats. Three matter for dogs:

  • EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid): the long-chain omega-3s found in fish oil and algal oil. VCA Animal Hospitals describes them as anti-inflammatory, which is why they are used for skin allergies, arthritis, kidney disease, heart disease and other inflammatory conditions.
  • ALA (alpha-linolenic acid): the plant omega-3 in flaxseed. A 2021 analysis of veterinary diets and supplements described ALA as the less active omega-3, and found that some products contained more ALA than EPA and DHA.

VCA describes fish oil as coming from cold-water fish such as salmon. Algal oil is a plant-based source: a 2019 study in Beagles found that an algal oil containing EPA and DHA raised blood levels of both and was well tolerated through pregnancy, nursing and growth.

Where the evidence is strongest: arthritis

Osteoarthritis is where omega-3 has been tested most:

  • Weight bearing: in a 2010 randomized, double-blinded trial of 38 dogs with arthritis, dogs fed a food containing 3.5% fish oil omega-3 put more weight on their worst leg after 90 days. Weight bearing improved in 82% of those dogs, compared with 38% on a typical food.
  • Daily life: in a 127-dog trial across 18 veterinary clinics, owners of dogs fed a high omega-3 food reported better ability to rise and play at 6 weeks and to walk at 12 and 24 weeks.
  • Less pain medication: in a 131-dog trial, dogs fed a fish-oil-supplemented food had their carprofen dose reduced significantly faster than dogs on a control food.
  • A supplement, not a food: a 2016 trial of 78 dogs gave fish oil providing an average of 69 mg of EPA plus DHA per kg a day, and found improvements in discomfort, lameness and joint scores compared with a placebo oil.

Not every trial was positive. A 2012 study of 77 dogs, which its authors describe as un-commissioned, found no significant difference between deep sea fish oil and corn oil on force-plate measurements or the main pain score, although owners in the fish-oil group were happier with the treatment.

Taken together, a 2012 systematic review found the evidence was poor for joint supplements in general, with the exception of omega-3-supplemented diets in dogs. A 2022 review of 72 trials found clear pain-relief evidence for omega-3-enriched diets and omega-3 supplements. The 2023 international COAST osteoarthritis guidelines state that essential fatty acids have the largest evidence base of nutritional supplements, and put omega-3 ahead of other nutraceuticals for dogs with arthritis.

Omega-3 works alongside pain treatment and weight control, not instead of them. See dog food for joint health and the best joint supplements for senior dogs.

Skin and allergies

  • A 2010 systematic review of treatments for atopic dermatitis found one high-quality trial in which an oral essential fatty acid supplement cut prednisolone use by about half.
  • In a 2004 trial of 29 allergic dogs, skin scores improved with flax oil or an EPA and DHA product over 10 weeks, but not with a mineral oil placebo.
  • The 2015 international treatment guidelines for canine atopic dermatitis list possibly increasing essential fatty acid intake as part of chronic care, alongside bathing and avoiding flare factors. The guidelines name medications such as glucocorticoids, ciclosporin and oclacitinib as the most effective treatments for chronic itch.

So omega-3 can help an allergic dog's plan, but it is rarely enough on its own.

Brain, heart and other uses

  • Puppies: in a 2012 study of 48 Beagle puppies, those fed a high-DHA fish oil food from weaning to one year did better on several learning and memory tasks. That food also contained more vitamin E, taurine, choline and carnitine, so the effect cannot be credited to DHA alone.
  • Older dogs: a 2017 study found that aged Beagles fed a DHA-rich algae improved on initial learning tasks, but not on long-term recall. Other senior studies tested blends, so they cannot isolate omega-3.
  • Heart failure: in a 1998 study of 28 dogs with heart failure, fish oil reduced an inflammatory marker and improved muscle wasting compared with placebo.

These are smaller or narrower studies. They justify a conversation with your vet, not a promise.

Does a healthy dog need an omega-3 supplement?

Usually not. Complete and balanced dog foods contain some omega-3, and the Merck Veterinary Manual notes that nutritional supplements are not required and can be harmful in some cases. In the COAST guidelines, most experts felt supplements were not needed for dogs at risk of arthritis but without signs, if the diet was balanced. For those dogs, the guidelines quote a National Research Council allowance for adult maintenance of 30 × body weight in kg to the power of 0.75, in mg of EPA plus DHA per day. For a 20 kg (44 lb) dog that works out to roughly 280 mg a day from all sources.

Dogs with diagnosed arthritis are different. COAST quotes 75 to 100 mg of EPA plus DHA per kg of body weight per day as a starting or minimum amount, which is 1,500 to 2,000 mg for a 20 kg dog, and sets an upper limit that should not be exceeded. Work out the total with your vet, counting what your dog's food already supplies. Our omega-3 dosage chart shows the arithmetic.

What about omega-3-6-9 blends?

Blends labeled omega-3-6-9 combine omega-3 with omega-6 and omega-9 fats. Dog foods already contain omega-6, so the useful question is still how much EPA and DHA a serving provides. In the 2004 allergy trial, neither total fatty acid intake nor the omega-6 to omega-3 ratio predicted which dogs improved. A blend that lists only "omega-3" or uses mainly flax may supply little EPA and DHA.

How to read an omega-3 label

  • Find EPA and DHA in mg per serving. A label that says "1,000 mg fish oil" with 180 mg EPA and 120 mg DHA provides 300 mg of EPA plus DHA, not 1,000 mg.
  • Check for vitamins A and D. Some fish oil products for dogs contain them. A 2025 analysis of dog fish oil products advised counting fat-soluble vitamins and selenium at higher doses.
  • Prefer independently tested products. The same 2025 analysis found six cases of products missing their EPA or DHA label claims by more than 5%.

More in our guide to the best omega-3 supplement for dogs.

How to choose a fish oil for your dog

Use the same checks for every bottle:

  • EPA and DHA per serving, in mg. Total "fish oil" or total "omega-3" alone does not let you compare products.
  • A clear serving size. Know exactly what one capsule, pump or measured liquid serving delivers, and how many your dog's weight needs.
  • The full ingredient list. Look for every active ingredient and its amount, with no proprietary blend hiding them.
  • What the food already supplies. Many senior and joint diets already contain added EPA and DHA, so count both together.
  • The real daily cost. Work out the price per labeled daily serving, not per bottle; a concentrated oil can be cheaper per day than a dilute one.
  • Cod liver oil is not the same thing. It also supplies vitamins A and D, which build up in the body, so it cannot be dosed like ordinary fish oil.
  • Human chewable supplements: check for xylitol. The US FDA lists dietary supplements and chewable vitamins among products that may contain this sweetener, which is dangerous to dogs.

Our guide to the best omega-3 supplement for dogs goes through these checks in detail, and the fish oil dosage chart turns them into amounts by weight.

Fish oil and green-lipped mussel

New Zealand green-lipped mussel is another marine source of omega-3, supplying EPA and DHA along with a less common omega-3, ETA. It has its own trial evidence for joints: in a 2006 trial, 67% of dogs with joint disease improved by day 56 on a green-lipped mussel extract, against 41% on placebo. Our green-lipped mussel powder is a single-ingredient topper that can sit alongside a fish oil in a joint plan. See green-lipped mussel for dogs: the evidence.

Side effects in brief

A veterinary review lists possible problems including altered platelet function, stomach upset, slower wound healing, weight gain from extra calories, oxidation of the oil and interactions with drugs. VCA advises caution in dogs on blood thinners or with clotting disorders, diabetes, a history of pancreatitis or diarrhea, and in pregnant or nursing dogs. See omega-3 side effects in dogs.

FAQ

How much fish oil should I give my dog?

Dose by EPA plus DHA, not by the amount of oil. For a dog with arthritis, the COAST guidelines quote 75 to 100 mg of EPA plus DHA per kg of body weight a day as a starting amount; a healthy adult needs far less. Count what the food already supplies, and see our dosage chart by weight.

How long does omega-3 take to work in dogs?

VCA notes that full effects may take several weeks. In the arthritis trials, owner-reported changes appeared from 6 weeks and force-plate changes were measured at 90 days.

Is salmon oil the same as fish oil?

Salmon oil is a fish oil. What matters is the EPA and DHA per serving, which varies between products.

Can I give my dog flaxseed oil instead?

Flax supplies ALA, the less active omega-3. If your goal is EPA and DHA, for example for arthritis, choose a fish or algal oil that states both amounts.

Is omega-3 good for older dogs?

It is most useful for older dogs with arthritis, which is common in seniors. It does not replace a vet exam for new stiffness, limping or behavior changes.

Is human fish oil safe for dogs?

It can be, but check it contains only fish oil, note the EPA and DHA amounts, and avoid products with added vitamins A and D unless your vet agrees. VCA advises against using fish oil without a reputable source, because of the risk of heavy metal contamination.

References

For individual health questions, your veterinarian remains the best partner.

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