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Fish Oil in Dog Diet: The Link to Diarrhea

Mar 12,2025 | puaintapets

Fish oil is widely recommended for dogs’ skin, joints, and overall health, but some pet owners notice that their dogs develop diarrhea after taking it. So, can fish oil cause diarrhea in dogs? The short answer is yes, but it depends on dosage, quality, and the dog’s individual sensitivity.

In this guide, we’ll explore the benefits and risks of fish oil, how to prevent diarrhea, and what to do if your dog has an upset stomach after taking it.

Fish Oil for Dog

Can Fish Oil Cause Diarrhea in Dogs?

Yes, fish oil can cause diarrhea in dogs, especially when given in high doses. Here's what you need to know:

How does fish oil cause diarrhea in dogs?

1. The reason of fish oil itself

Excessive concentration of fish oil: If the concentration of fish oil fed to your dog is too high, it may cause diarrhoea as your dog's stomach and intestines are unable to adapt.

Fish oil type not adapting: Dogs may not adapt to specific types of fish oil, such as certain brands or sources, and switching to other types of fish oil may improve the situation.

Fish oil quality problem: low quality or contaminated fish oil may contain impurities, heavy metals and other harmful substances, which may irritate your dog's intestines and cause diarrhoea.

2. Dog's own reasons

The body has not adapted to the new food: the dog's body may take some time to adapt to the new nutrient, fish oil, and may experience diarrhoea and other uncomfortable reactions during the adaptation period.

Intolerance to fish or fish products: Some dogs may be allergic or intolerant to fish or fish products, and fish oil, as a type of fish product, may also cause diarrhoea.

Digestive problems: Dogs themselves have a sensitive digestive system or diseases, such as enteritis, gastritis, etc. Fish oil may aggravate these problems and cause diarrhoea.

3. Improper feeding methods

Overdose: Feeding your dog a dose of fish oil that exceeds its body's tolerance may lead to diarrhoea.

Feeding on an empty stomach: Fish oil is best fed after a meal. If you feed your dog fish oil on an empty stomach, it may cause gastrointestinal discomfort and lead to diarrhoea.

Improper combination with other foods: Certain foods may affect your dog's digestion when paired with fish oil, for example, foods that contain a lot of magnesium (e.g. avocado, tofu, etc.), magnesium itself has a softening effect on the stool, which may exacerbate diarrhoea.

dog fish oil

What Are The Other Side Effects Of Fish Oil In Dogs?

Gastrointestinal issues

Diarrhea: High doses of fish oil can cause diarrhea in dogs, especially those with sensitive digestive systems.
Vomiting: Some dogs may vomit after taking fish oil, particularly if given on an empty stomach or in excessive amounts.
Digestive upset: Other signs of digestive discomfort, such as stomach upset, acid reflux, or indigestion, may also occur.

Also Read: Dog Diarrhea Home Remedy: Best Remedy For Dog Diarrhea

Skin and coat problems

Skin irritation: In some cases, fish oil may cause skin irritation or a change in coat color.
Dry, flaky skin: Although fish oil is often used to improve skin health, in some dogs, it may initially cause dryness or flakiness before the beneficial effects become apparent.

Blood clotting and bleeding risks

Altered platelet function: Fish oil can thin the blood, potentially increasing the risk of bleeding, especially in dogs with bleeding disorders or those taking anticoagulant medications.
Delayed wound healing: High doses of fish oil may interfere with the normal blood clotting process, leading to slower wound healing.

Other potential side effects

Weight gain: Excessive consumption of fish oil may contribute to weight gain in some dogs.
Tiredness or lethargy: Some dogs may experience increased tiredness or lethargy after starting fish oil supplementation.
Increased risk of pancreatitis: In rare cases, fish oil may increase the risk of pancreatitis, especially in dogs with pre-existing pancreatic problems.

It's important to note that these side effects are not common and most dogs tolerate fish oil well when given in appropriate doses. However, if any of these symptoms occur, it's crucial to consult a veterinarian immediately.

What Are the Benefits of Fish Oil for Dogs?

1. Skin and coat health

Improve skin condition: Omega-3 fatty acids in fish oil have anti-inflammatory properties, which can reduce skin inflammation, relieve itching, redness and swelling, and have a therapeutic effect on skin diseases such as canine atopic dermatitis, flea bite hypersensitivity and food allergies.
Make the coat healthier: fish oil can increase the moisture content of skin cells, making the coat softer, smoother and shinier, while reducing hair shedding and breakage.

2. Joint health

Reduces joint inflammation: Omega-3 fatty acids can inhibit the inflammatory response within the joints, reducing pain and swelling, and providing some relief for dogs suffering from osteoarthritis, rheumatoid arthritis, and other joint diseases.
Enhance joint flexibility: Fish oil can promote the repair and regeneration of joint cartilage, increase the secretion of joint fluid, and improve joint flexibility and mobility.

Also Read: 2025 The Best Hip and Joint Supplement for Dogs

3. Cardiovascular health

Lower blood lipids: Omega-3 fatty acids in fish oil can lower triglyceride and cholesterol levels in the blood, reducing the risk of atherosclerosis and preventing cardiovascular disease.
Improve Blood Circulation: Fish oil can dilate blood vessels, reduce blood viscosity and promote blood circulation, which is an aid to dogs suffering from cardiovascular diseases such as heart disease and high blood pressure.

4. Immune system health

Enhance immunity: Omega-3 fatty acids in fish oil can regulate the function of the immune system, enhance the body's resistance and prevent infections and diseases.
Relieve allergic reactions: Fish oil can reduce the occurrence of allergic reactions, and has a soothing effect on dogs suffering from allergic diseases.

5. Brain and nervous system health

Promote brain development: DHA in fish oil is an important part of the brain and retina, and is important for brain development and vision development in puppies.
Improve Cognitive Function: Fish oil can improve the cognitive ability and memory of the brain, and has a certain effect on the cognitive decline of older dogs.
Relieves anxiety and depression: Omega-3 fatty acids in fish oil can regulate the balance of neurotransmitters and relieve emotional problems such as anxiety and depression.

6. Kidney Health

Protect kidney function: Omega-3 fatty acids in fish oil can reduce kidney inflammation and oxidative stress, protect kidney function, and have a certain auxiliary therapeutic effect on dogs with chronic kidney disease.

How to Choose the Right Fish Oil for Your Dog?

Choosing the right fish oil for your dog can start with a few things:

I. Ingredients and purity

Omega-3 content

Choose a fish oil with high Omega-3 content, of which EPA and DHA are the key components, which have many health benefits for dogs, such as improving skin and coat health, boosting immunity, and protecting joints.

Purity

Try to choose fish oil with high purity to reduce the intake of impurities and other unnecessary ingredients.

II. Quality and Safety

Brand reputation

Choose fish oils from well-known brands, whose production process and quality control are more guaranteed.

Source of raw materials

Choose fish oil from quality fish and avoid contaminated fish oil.

Testing and Certification

Ensure that the fish oil has undergone strict quality testing and meets the relevant safety standards.

Fish Oil Concentrate for Dogs and Cats

The Fish Oil Concentrate is rich in high-concentration omega-3 unsaturated fatty acid, which helps to nourish dogs' and cat's skin and give health support for their hair or coat, joint, heart and physical state.

View Product

III. Individual needs of dogs

Health conditions

If the dog has specific health problems, such as skin allergies, joint diseases, etc., choose fish oils with appropriate efficacy.

Age and weight

According to the dog's age and weight, choose the appropriate dose of fish oil.

IV. Product Format and Packaging

Product form

Fish oil products are available in liquid, capsule, soft chewable tablets and other forms, choose the form suitable for your dog.

Packaging

Choose fish oil products that are well packaged, protected from light and sealed to prevent oxidation of the fish oil.

How to Prevent Diarrhea When Giving Fish Oil to Dogs

To prevent diarrhea when giving fish oil to dogs, consider the following steps:

Dosage and Administration

Consult Your Veterinarian: Before starting your dog on fish oil supplements, consult your veterinarian. They can recommend the appropriate dosage based on your dog's size, age, and health condition.
Start Slowly: Begin with a small dose and gradually increase it over a week or two to allow your dog's digestive system to adjust.
Administer with Food: Give the fish oil with your dog's meal to help reduce the likelihood of stomach upset.

Product Selection

Choose High-Quality Fish Oil: Select a reputable brand that uses purified fish oil to reduce the risk of contaminants.
Consider Alternatives: If your dog is sensitive to fish oil, explore alternative sources of omega-3 fatty acids, such as krill oil or algae-based supplements.

Monitoring and Adjustment

Watch for Signs of Digestive Upset: Keep an eye out for any signs of diarrhea, vomiting, or other digestive issues. If these occur, stop giving the fish oil and consult your vet.
Adjust the Dosage: If your dog experiences mild digestive upset, your vet may recommend reducing the dosage or adjusting the frequency of administration.
Monitor Overall Health: Regularly assess your dog's overall health and consult your vet if you notice any changes or concerns.

FAQs

Can I stop giving my dog fish oil if it causes diarrhea?

Yes! Try reducing the dosage or switching to an alternative source of omega-3s.

How long does diarrhea from fish oil last?

Mild diarrhea should improve within a few days. If it persists, stop the supplement and consult a vet.

Are there any alternatives to fish oil for dogs?

There are some plant - based omega - 3 sources, such as flaxseed oil. However, these may not provide the same type and amount of EPA and DHA as fish oil. Some dog foods are also fortified with omega - 3 fatty acids.

Conclusion

Fish oil can be a beneficial addition to a dog's diet due to its rich omega - 3 content. However, it may also be linked to diarrhea. The reasons are multiple. High - concentration, poor - quality fish oil, or the dog's individual intolerance can cause digestive problems. When introducing fish oil, proper dosage, starting slowly, and giving it with food are important. Also, choosing high - quality products and monitoring the dog's reaction are crucial. Overall, while fish oil offers potential health benefits for dogs, caution should be exercised to avoid diarrhea and ensure its positive impact on the dog's well - being.