For a healthy adult dog, a common starting point is about 50 mg of combined EPA and DHA per kilogram of body weight per day, which works out to roughly 1,400 mg for a 60 lb dog, a number worth checking yourself since the bottle rarely states it plainly. Dogs with arthritis are often dosed higher, up to a ceiling that a veterinary teaching hospital sets at about 3,700 mg for that same 60 lb dog. This post covers what fish oil does with real evidence behind it, how to dose by weight, the upper limit, and how to pick a bottle that is not already rancid.
What fish oil actually does for dogs
Fish oil is the supplement with the most evidence behind it in dogs, and even that evidence is narrower than the marketing. The active parts are two long chain omega 3 fatty acids, EPA and DHA. Dogs cannot make enough of them from plant oils like flax, so if you want them in the dog, they need to come from fish, krill, or algae.
The strongest case is joint pain. A 2022 systematic review and meta analysis in the International Journal of Molecular Sciences pooled 72 trials of diets and supplements for osteoarthritis in pets, and omega 3 fatty acids came out as the category with clear analgesic efficacy, in both enriched diets and standalone supplements.1 The Merck Veterinary Manual's osteoarthritis chapter says the same thing in plainer terms: EPA supplementation and EPA rich diets have been shown to improve gait and mobility.2
Beyond joints, the Tufts Cummings School's Clinical Nutrition Service lists heart disease and kidney disease as conditions where omega 3s have shown clinical benefits in dogs, including reduced protein in the urine in kidney patients.3 Skin and coat is where owners most often notice a difference, and it is a reasonable use, but the joint and heart data are the parts I would call solid. If itch is the problem, start with the common causes of itchy skin in dogs, because fish oil will not fix fleas or a food allergy.
How much fish oil should I give my dog?
Dose by EPA plus DHA, never by milliliters or milligrams of "fish oil." A 1,000 mg fish oil capsule might contain 300 mg of EPA and DHA, or 600 mg, depending on the concentration. The number you want is on the back of the bottle.
A 2020 review in Today's Veterinary Practice by two board certified veterinary nutritionists puts the therapeutic range at 50 to 220 mg of EPA plus DHA per kilogram of body weight per day, with the top of that range reserved for osteoarthritis.4 Colorado State University's veterinary hospital publishes a dosing chart for dogs with osteoarthritis that caps the daily dose using metabolic body weight, and it tells owners to start at about a quarter of the maximum and increase slowly while watching for loose stools and vomiting.5
| Dog weight | Everyday starting dose (about 50 mg/kg) | CSU maximum for arthritis |
|---|---|---|
| 20 lb | about 450 mg | 1,623 mg |
| 40 lb | about 900 mg | 2,730 mg |
| 60 lb | about 1,360 mg | 3,700 mg |
| 80 lb | about 1,800 mg | 4,591 mg |
| 100 lb | about 2,270 mg | 5,427 mg |
All figures are combined EPA plus DHA per day. The starting column is my arithmetic from the low end of the published range; the maximum column is copied from the CSU chart.5 Notice that the two sources scale differently. That is not an error. One uses straight body weight and the other uses metabolic body weight, and both are legitimate. It is a good reminder that fish oil dosing is a range with judgment in it, not a formula carved in stone.
Is there such a thing as too much?
Yes. The National Research Council sets a safe upper limit for dogs of 280 mg of combined EPA and DHA per 100 kcal of food eaten.4 For a 60 lb dog eating around 1,100 kcal a day, that is a ceiling near 3,100 mg, which sits close to the CSU arthritis maximum. Going past it is where the downsides show up. The Today's Veterinary Practice review lists altered platelet function, GI upset, slower wound healing, weight gain from the extra calories, and possible effects on immune function and insulin sensitivity.4 Tufts adds that fish oil is not appropriate for every dog, specifically those with gastrointestinal or bleeding disorders.3
Two practical points. First, fish oil is fat, and fat is calories. A 60 lb dog at the arthritis dose is taking in something like 35 to 45 extra calories a day, which matters if the dog is already carrying weight, and most arthritic dogs are. Second, if your dog eats a food that already includes fish oil, count that toward the total. Some therapeutic diets contain a lot.
How to choose a fish oil that is not already rancid
This is the part most guides skip. Omega 3s oxidize fast when exposed to air, heat, and light, and an oxidized oil is at best useless and at worst mildly pro inflammatory. Tufts is blunt about the supplement market in general: the FDA does not review supplements for effectiveness, safety, or quality before they are sold, and studies have found products containing double the labeled amount or none of it.6
- Look for a third party certificate of analysis. CSU recommends products whose labels show EPA and DHA amounts and whose makers can produce third party testing.5 If a brand cannot show you a certificate of analysis, move on.
- Buy small, dark bottles or capsules. A liquid pump bottle that sits open on the counter for three months is a chemistry experiment. Capsules protect the oil until you use it.
- Refrigerate after opening and use liquids within the window the label states.
- Smell it. Fresh fish oil smells faintly of the ocean. Sharp, paint like, or strongly fishy means it has turned. Throw it out.
- Skip cod liver oil as a daily omega 3. It carries a lot of vitamin A and D, and those fat soluble vitamins accumulate.
Whole fish is a legitimate alternative to a bottle. We covered the math in our post on sardines for dogs. Every omega 3 product we list in our supplements collection has to show us third party testing and pass The Truva Standard at a B or better, and we still tell you to check the EPA plus DHA per serving yourself.
The honest limitation
Fish oil helps arthritic dogs move better. It does not rebuild cartilage, it does not replace pain medication in a dog that is hurting, and the Merck chapter is clear that NSAIDs remain the most predictably effective treatment for osteoarthritis.2 Weight matters more than any supplement. If your senior dog is stiff, read our guide to managing arthritis in senior dogs and put fish oil in its proper place: a useful tool, not the plan, and not something to buy just because a bottle promises more than the evidence does.
When to call the vet
Ask your vet before starting fish oil if your dog is on an NSAID, a blood thinner, or has a history of pancreatitis, bleeding problems, or chronic GI disease. Stop and call if you see vomiting, diarrhea that lasts more than a day, or any unusual bruising or bleeding. If you are dosing for arthritis, get the dose from your vet rather than the chart, because they know your dog's kidneys, weight, and medications.
Sources
- Barbeau-Grégoire M et al., "A 2022 Systematic Review and Meta-Analysis of Enriched Therapeutic Diets and Nutraceuticals in Canine and Feline Osteoarthritis," International Journal of Molecular Sciences, 2022. mdpi.com
- Merck Veterinary Manual, "Osteoarthritis in Dogs and Cats," reviewed 2025. merckvetmanual.com
- Tufts Cummings School Clinical Nutrition Service (Petfoodology), "Should I give fish oil to my pet?," 2018. sites.tufts.edu/petfoodology
- Raditic D and Gaylord L, "Fish Oil Dosing in Pet Diets and Supplements," Today's Veterinary Practice, 2020 (updated 2024). todaysveterinarypractice.com
- Colorado State University Veterinary Health System, "Canine fish oil dosing chart." csuveterinaryhealth.org
- Tufts Cummings School Clinical Nutrition Service (Petfoodology), "Dietary Supplements for Pets: Harmful or Helpful?," 2017. sites.tufts.edu/petfoodology