Fish Oil for Dogs

Fish oil is a very safe supplement for dogs. It provides omega-3 fatty acids that have well documented anti-inflammatory properties. Veterinarians recommend fish oil for dogs with a variety of challenges including cancer, skin disease, arthritis, kidney disease, and cardiovascular disease.

Key Takeaways

  • You may give your dog fish oil formulated for humans. Just take care that it is from a good quality manufacturer and does not have any other ingredients in it that would be unsafe for your dog. You can contact your veterinarian to help establish the proper dose.
  • Fish oil for dogs is based on metabolic weight thus the calculation is a bit more complicated than usual. There is also a large dosage range in dogs that depends on the condition being treated. For instance, fish oil for arthritis is a much higher dose than fish oil for kidney disease. Some general guidelines for dosage can be found on dog specific products. If you are going to use a human product, please talk to your vet about the proper dosage.
  • Fish oil is safe to give to your dog every day.
  • The most common side effects of fish oil in dogs are gastrointestinal signs including diarrhea and vomiting.
  • Fish oil for dogs has many benefits. It contains omega-3 fatty acids that have well documented anti-inflammatory properties. Fish oil can be helpful for dogs with a variety of health challenges including skin disease, osteoarthritis, kidney disease, cancer, and cardiovascular disease.

Fish Oils Are a Good Source of Omega-3 Fatty Acids for Dogs

Fish oil comes from the oils of fish and shellfish. Veterinarians recommend fish oil for dogs for a variety of reasons, including cancer, skin disease, heart disease, and others.

Fish oil has a high concentration of long chain fatty acids. Long chain fatty acids have different names and properties depending on how many carbon molecules are in the chain and the location and number of double bonds. Omega-6 fatty acids are considered pro-inflammatory while omega-3 fatty acids are considered anti-inflammatory.

The Benefits of Fish Oil for Dogs

Omega-3 fatty acids are essential to healthy cellular function in dogs. Supplementation can improve receptor and cell ion membrane function as well as decrease inflammation.

  • The inflammatory response is muted by decreasing the concentration of arachidonic acid (a pro-inflammatory omega-6 fatty acid).
  • Arachidonic acid is broken down in the body to prostaglandins and leukotrienes which are both inflammatory cell mediators.
  • Supplementation with fatty acids decreases the amount of arachidonic acid in turn decreasing the concentrate of inflammatory mediators.
  • Increased levels of omega-3 fatty acids also result in decreased expression of other inflammatory mediators such as TNF-alpha and COX-2.7

This decrease in inflammation is why DHA and EPA, discussed below, are thought to help in many different inflammatory diseases including cancer.


DHA (docosahexaenoic acid) and EPA (eicosapentoaenoic acid) are two important Omega-3 fatty acids. They are considered polyunsaturated (meaning they have two or more double bonds). It is these Omega 3 fatty acids that are plentiful in fish oil and have been shown to have significant anti-inflammatory effects and positive health effects.


ALA (alpha-linolenic acid) is another omega-3 fatty acid found in plant oils (such as flax, soy, canola) but it does not have the same physiologic effects as DHA and EPA. So, when choosing supplements for your dog stick with fish oil rather than plant-based oils.

Cod Liver Oil

It is also important to avoid fish liver oils such as cod liver oil. Even though it is a good source of EPA/DHA it can contain varying amounts of vitamins A and D. These vitamins can be toxic at high levels and should only be supplemented if bloodwork shows they are necessary.

Fish Oil Supplements for Dogs

Fish oil comes in either capsule or liquid form and does not require a prescription. Fish oil for dogs is widely available from a variety of manufacturers. As with any supplement, it is not regulated like a medication is, so make sure the product you have chosen is from a well-researched and well-regarded source.

Most veterinary offices sell a fish oil product they are confident in so you can ask your veterinarian for a recommendation. Common veterinary brands include Welactin®, Eicosaderm®, Dermapet®, Free Form Omega-3 Snip Tips®, and Nordic Naturals®.

Fish oils can also be found in health food stores. Please keep in mind that concentrations of fatty acids will vary with products so check with your veterinarian before giving them to your pet so you can ensure the proper dosage.

Common Uses for Fish Oil for Dogs

Fish oil may help in the management of:

  • Allergic Dermatitis
  • Immune mediated skin disease
  • Osteoarthritis
  • Cardiovascular disease
  • Kidney Disease
  • Hyperlipidemia (high triglycerides)
  • Cancer

Evidence for Efficacy of Fish Oil in Dogs

The exact mechanism of how fatty acids have anti-tumor effects is still being investigated. There is evidence in humans that fish oil supplementation can help the treatment of colon, breast, and prostate cancers.1

Cell Membrane Theory

One theory on how fatty acids help with cancer focuses on cell membrane (the outside of the cell) health. Cell membranes are made of lipids which can be attacked by free radicals. This is called lipid peroxidation.

DHA is an easily peroxidizable lipid. When you give fish oil to your dog, the DHA becomes incorporated into the cancer cell membranes which makes them more susceptible to dying from lipid peroxidation. A study investigating this theory supplemented patients on chemotherapy for metastatic breast cancer with DHA and found improved outcomes.3

A clinical trial looking at omega-3 fatty acid supplementation in dogs with lymphoma also found improved outcomes. In this study, dogs with lymphoma received chemotherapy and a diet supplemented with menhaden fish oil (140 g EPA and 120 g DHA) as well as arginine. The dogs who were supplemented revealed longer survival times and longer disease-free intervals.9

Omega-3s and Apoptosis

Fatty acids may also prevent the development of carcinogen induced tumors, cancer cachexia (weight loss), and metastasis.

Again, the exact mechanism is unclear, but EPA may have the ability to induce cancer cell death (apoptosis) and decrease cancer cell reproduction.

Human studies also show a protective mechanism for colon cancer.4

Improves Chemotherapy Effectiveness

Furthermore, supplementation with fatty acids has been shown to improve the effectiveness of chemotherapy.8

Safety and Side Effects

The most common side effects of fish oil are gastrointestinal and include belching, vomiting, and diarrhea.

Less common but more serious side effects can include increased clotting times due to a modulation of platelet function which may present as bleeding or bruising. Other less common serious side effects are pancreatitis (inflammation of the pancreas), and delayed wound healing.

There are some studies that showed alteration in blood glucose, but the research here is unclear. In cats, studies suggest it can improve glucose control while some human studies show the opposite.

There is also theoretical concern that fish oil can alter immune function but clinical evidence for this is lacking.

Another side effect that won’t bother your dog, but may bother you, is a fishy smell to their fur or breath!

Using Fish Oil with Other Treatments

Fish oil is generally safe to be given with most medications with some exceptions (listed below).

It is safe to be given with chemotherapy unless otherwise directed by an oncologist.

Make sure your dog is tolerating fish oil before starting other medications, so you are aware which medication is causing a reaction. This is of most importance regarding gastrointestinal side effects. Starting fish oil slowly and working up to a full dose over time will help your dog adjust and help with tolerance.

When to Not Use Fish Oils for Dogs

There are instances in which you shouldn’t use fish oil for dogs or should use it with caution.

  • Do not give if your dog has bleeding disorder or coagulation issues.
  • Do not give if patient is on blood thinners or aspirin.
  • Use with caution when giving in conjunction with non-steroidal anti-inflammatory drugs (NSAID).
  • Use caution if dog has a history of pancreatitis or significant bouts of diarrhea.
  • In pregnant or lactating animals please speak with a veterinarian before using.
  • Use caution with pets on a diet that already has high amounts of supplemented fatty acids such as a joint diet, as this may over supplement.

In general, contact your veterinarian to help discern the total dosage.

How to Give Fish Oil

Fish oil is available as a capsule or in a liquid form. Give it once daily orally with or without food. If given without food and vomiting occurs, then give with food.

Be careful with liquid dosing as you can overdose if not measuring carefully.

Dosages are based primarily on metabolic weight and can vary depending on the condition being treated so consult your veterinarian for appropriate dosing.

What If I Miss a Dose?

Give the next dose as prescribed. Do not double up on dosage or administer too close to the next dose as this may cause unwanted side effects (primarily gastrointestinal).

Storage and Handling

Fatty acids are sensitive to oxidative damage so they should be stored in a cool, airtight, container with protection from light.

Our Take on Fish Oil for Dogs

Overall fish oil is a very safe supplement and can have added benefit for other conditions that canine cancer patients often have due to age such as osteoarthritis, cardiovascular disease, and chronic kidney disease.

The evidence directly related to cancer is limited in canine models and the one study on lymphoma also supplemented with arginine, so it is hard to know how effective the DHA alone was.

The evidence for humans is also limited, but the research is promising.

The evidence for the anti-inflammatory actions of Omega-3 fatty acids is voluminous and quite definitive. Given we know that cancer is an inflammatory disease process, the use of Omega-3 fatty acids seems warranted and even better if there may be bonus anti-tumor effects.

Given the many positive effects of fish oil, if patients tolerate it well and do not have contraindicated conditions or medication, we think it is a good supplement to add to the toolbox for supportive care for canine cancer.

  1. Attar-Bashi NM, Orzeszko K, Slocombe RF, Sinclair AJ. Lipids and FA analysis of canine prostate tissue. Lipids. 2003;38(6):665-668. doi:10.1007/s11745-003-1112-y
  2. Bauer JE. Therapeutic use of fish oils in companion animals. J Am Vet Med Assoc. 2011;239(11):1441-1451. doi:10.2460/javma.239.11.1441
  3. Bougnoux P, Hajjaji N, Ferrasson MN, Giraudeau B, Couet C, Le Floch O. Improving outcome of chemotherapy of metastatic breast cancer by docosahexaenoic acid: a phase II trial. Br J Cancer. 2009;101(12):1978-1985. doi:10.1038/sj.bjc.6605441
  4. Deschner EE, Lytle JS, Wong G, Ruperto JF, Newmark HL. The effect of dietary omega-3 fatty acids (fish oil) on azoxymethanol-induced focal areas of dysplasia and colon tumor incidence. Cancer. 1990;66(11):2350-2356. doi:10.1002/1097-0142(19901201)66:11<2350::aid-cncr2820661117>;2-6
  5. Lenox CE, Bauer JE. Potential adverse effects of omega-3 Fatty acids in dogs and cats. J Vet Intern Med. 2013;27(2):217-226. doi:10.1111/jvim.12033
  6. Lenox CE, Bauer JE. Potential adverse effects of omega-3 Fatty acids in dogs and cats. J Vet Intern Med. 2013;27(2):217-226. doi:10.1111/jvim.12033
  7. Magalhães TR, Lourenço AL, Gregório H, Queiroga FL. Therapeutic Effect of EPA/DHA Supplementation in Neoplastic and Non-neoplastic Companion Animal Diseases: A Systematic Review. In Vivo. 2021;35(3):1419-1436. doi:10.21873/invivo.12394
  8. Nabavi SF, Bilotto S, Russo GL, et al. Omega-3 polyunsaturated fatty acids and cancer: lessons learned from clinical trials. Cancer Metastasis Rev. 2015;34(3):359-380. doi:10.1007/s10555-015-9572-2
  9. Ogilvie GK, Fettman MJ, Mallinckrodt CH, et al. Effect of fish oil, arginine, and doxorubicin chemotherapy on remission and survival time for dogs with lymphoma: a double-blind, randomized placebo-controlled study. Cancer. 2000;88(8):1916-1928.
  10. Xenoulis PG, Steiner JM. Lipid metabolism and hyperlipidemia in dogs. Vet J. 2010;183(1):12-21. doi:10.1016/j.tvjl.2008.10.011
  11. Plumb DC. Fatty Acids, Omega-3. Plumb’s Veterinary Drugs. Updated August 2021. Accessed November 14, 2022
  12. Lenox C. Role of Dietary Fatty Acids in Dogs & Cats. Today’s Veterinary Practice. Published August 16, 2016. Accessed April 10, 2023.
  13. Lee J. Using Fish Oil in Dogs and Cats | VetGirl Veterinary CE Blog. VETgirl. Accessed April 10, 2023.
  14. Omega-3 Supplements: In Depth. National Center for Complementary and Integrative Health. Published May 2018. Accessed April 10, 2023.

Welactin® is a registered trademark of Nutramax Laboratories, Inc.
Eicosaderm® and Dermapet® is a registered trademark of Dechra Veterinary Products LLC.
Free Form Omega-3 Snip Tips® is a registered trademark of Bayer
Nordic Naturals® is a registered trademark of Nordic Pharma.



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