Are there side effects of taking too much fish oil?

Just because fish oil supplements are good for you doesn’t mean more is even better. Side effects like indigestion, heartburn, and bad breath typically show up on high doses of these supplements. Let’s look at how much fish oil is too much and what side effects to look out for. 

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When we talk about fish oil, we're referring to omega-3 fatty acids that you get from supplements or eating fish. You’ll find omega-3s in fatty fish like mackerel, salmon, sardines, herring, tuna, and cod liver, as well as fish oil capsules found at your local drug store. 

There are different types of omega-3 fatty acids, but two of the most important ones are called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). They might be a mouthful, but these polyunsaturated fatty acids can help with all types of health issues like preventing and even reversing heart disease (Novotny, 2022).

If you follow a vegan or vegetarian diet, you can get what’s called alpha-linolenic acid (AHA), a type of omega-3 derived from algae or flaxseed oil. 

It's worth noting that fish oil is generally well-tolerated. Even though fish oil supplements have health benefits like reducing inflammation and lowering blood pressure, taking too much can have adverse effects. Most people experience side effects on high doses of fish oil, while others may notice them taking lower amounts. Let’s look into some of the more common side effects. 

Unpleasant smelling breath

Sometimes the taste of fish oil supplements is hard to swallow, even for fish lovers. Vitamin burps don't just happen with fish oil and can be a sign that whatever you took is breaking open before it hits your digestive tract. 

Most of this is anecdotal, but many people report belching, fishy breath, and unpleasant-smelling sweat when taking fish oil. While storing your supplements in the fridge can lessen or dull the fishy flavor, it may not prevent the smell from sweating out during a workout.

Gastrointestinal trouble

Digestive issues are some of the most common side effects of omega-3 supplements, specifically indigestion, heartburn, diarrhea, nausea, and flatulence. Depending on the type of omega-3 fatty acids you take, other side effects you may notice include constipation, taste changes, and vomiting (Novotny, 2022; Khodarahmi, 2016).

Vegans looking to get their omega-3s through algae or flaxseed oil aren't immune from similar side effects. In fact, flaxseed oil may increase bowel movements enough to make it a viable treatment for constipation (Ramos, 2015).

Allergic reactions

Despite what you might think, it's rare for people allergic to fish or shellfish to also have an allergy to pure fish oil. However, if you have known fish or shellfish allergies, you may want to consider using flaxseed or algae oil as an alternative. You can also discuss the risks with your healthcare provider (Novotny, 2022).

There are other purported side effects of fish oil, but there simply isn't enough research to support them as fact. Here are other adverse effects claimed by some, although again, the scientific evidence on this is limited:

• Increased risk of bleeding, especially when taking anticoagulants (blood thinners)

• Bleeding in the stomach or intestines (ulcers)

• Stroke

• Vitamin A toxicity

• Insomnia

• Higher risk of prostate cancer

• Low blood pressure

Interestingly, the ability of fish oil to lower blood pressure is one of its many health benefits. That said, there is a chance that this could be dangerous for people who don’t have high blood pressure. 

How much is too much fish oil?

According to the Office of Dietary Supplements (ODS), the recommended daily intake of omega-3 fatty acids is 1,100 mg for women and 1,600 mg for men (OSD, 2021). 

Many people take fish oil supplements because of the potential health benefits. Some common uses and conditions fish oil may help with include (Novotny, 2022; OSD, 2021):

• High triglyceride (cholesterol) levels

• Heart disease

• Inflammatory conditions like rheumatoid arthritis

• Depression

• Cancer prevention

• Dry eye

• Alzheimer’s disease

• Age-related macular degeneration (AMD)

• Promoting maternal and fetal health during pregnancy

Taking the recommended dose of fish oil is not likely to cause serious side effects. Know that if you start taking higher doses, you’ll see more side effects than if when staying within the recommended range. Your healthcare provider can give you medical advice regarding the risks and benefits of fish oil supplementation. 

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

March 03, 2022

Written by

Linnea Zielinski

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.