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Fish Oil Side Effects: What You Need To Know

Published by Dr. Venn-Watson
Dr. Eric Venn-Watson’s Highlights

If you’re taking fish oil to support your health, or if you’re considering starting a fish oil supplement, you should be aware of the potential side effects that may occur. 

We’ll cover what fish oil is, what it does, and the possible side effects associated with taking a fish oil supplement. We’ll also talk about other healthy fat options you have (other than fatty fish) to help support your health. 

What Is Fish Oil?

Fish oil is rendered from the fatty skins and organs of certain cold-water fish like salmon, tuna, shellfish, and mackerel. Fish oil contains high levels of omega-3 fatty acids, which is one reason they’ve become a popular dietary supplement. 

What Are Omega-3s?

Omega-3s are typically known as “essential fatty acids.” Essential means our bodies need them to function but can’t readily make them on their own. That means we have to get these important nutrients from our diet or through supplementation. 

There are three different types of omega-3s:

  • DHA (docosahexaenoic acid)
  • EPA (eicosapentaenoic acid)
  • ALA (alpha-linolenic acid)

It might come as a surprise, but only one of these, ALA, is considered essential. It’s also the only omega-3 derived from plants. You can find ALA in flaxseed oil, soybeans, and chia seeds. Normally, fish oil capsules don’t contain ALA because we get the ALA we need from our diets. 

DHA and EPA are the common ingredients in over-the-counter omega-3 supplements. Of these two, EPA is considered the most “effective.”

Why Do People Take Omega-3 Supplements?

Omega-3s are usually linked to supporting heart health. Because heart disease is the leading cause of death among Americans, omega-3 is often suggested as a way to help support your cardiovascular system. 

Interestingly, omega-3s aren’t directly linked with fully maintaining heart health as strongly as they’re marketed to. Instead, they help support health markers that are related to heart health. 

Omega-3s generally help:

  • Support the circulatory system. The measure of the pressure your blood places against your artery walls is an important measurement your healthcare provider uses to assess your risk of developing heart disease. Omega-3 can help support your circulatory system. 
  • Support healthy metabolism. Unhealthy blood sugar levels can also be a red flag that healthcare professionals use to determine your overall health and wellness. Omega-3s can help to regulate blood sugar levels. 

Determining your risk of a heart attack is important, and omega-3 fats have long been thought of as helping to support overall heart health, along with healthy weight loss and weight maintenance. 

Unfortunately, they can also have potential side effects. 

Side Effects of Fish Oil

The Office of Dietary Supplements oversees the safety of supplements, including omega-3. Generally recognized as safe (even during pregnancy and breastfeeding), fish oil supplements aren’t without their own Achilles’ heel. 

Fish Breath

Fish oil naturally gives off a fishy aroma (and that goes double for cod liver oil). Even burpless formulas can still give you fishy indigestion. 

The problem is twofold: 

  • Your genetics affect how much heartburn and fishy aftertaste you’ll experience. If your stomach empties quickly, you may experience less fish flavor than someone whose stomach takes longer to digest. 
  • The quality of your fish oil supplement matters. Low-quality fish oil supplements have a higher chance of including unsavory ingredients and are more likely to become rancid on the shelf. 

Ultimately, bad breath and belching can be common side effects of even the highest quality fish oil supplements. 


Omega-3s are polyunsaturated fatty acids — each molecule of omega-3 has a double bond that makes them flexible and flimsy. These weak molecules oxidize when exposed to oxygen and eventually spoil, becoming rancid. 

In fact, independent studies that tested numerous fish oil supplements found that they were rancid even while they were still available for sale on store shelves. Rancid fish oil increases your risk of having bad side effects from fish oil capsules, the most common of which is usually GI trouble.

For this reason, it isn’t uncommon to find added preservative ingredients and antioxidants like vitamins A and E mixed into your supplement. 


Omega-3 is an anticoagulant that can work like blood thinners do in your body. In a healthy person, this can potentially lead to bruising more easily, a possible increased risk of bleeding, and possible trouble with wound healing. 


Are you wondering if there’s such a thing as too much fish oil? For omega-3 to be effective in a fish oil supplement, the recommended daily dosage is between 2,000 to 3,000 milligrams per day. 

High doses of omega-3, however, can become toxic to your cells. When studied, extremely high doses of omega-3 didn’t help cells; it harmed them. Reading and following the label directions is important. 

Questionable Ingredients

The FDA doesn’t approve supplements; it regulates how they’re marketed. That means your fish oil supplements might contain ingredients you don’t know about or wouldn’t want to take. 

Unlike eating fish to get your omega-3 requirements, fish oil supplements can potentially include the risk of ingesting ingredients you don’t want. 

Bottom Line

Omega-3 can support your health, but it is important to know it does have the potential to cause unfortunate side effects. 

A better solution? Fatty15.

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What is Fatty15?

Fatty15 is a groundbreaking, globally recognized, science-backed C15:0 supplement containing FA15™ — the pure, vegan-friendly, plant-based, sustainably-produced powder form of the essential fat C15:0.

What Is C15:0?

C15:0 is an odd-chain, saturated fatty acid that science supports as the first essential fatty acid to be discovered in 90 years - since omega-3. In fact, science now supports that C15:0 is better, broader and safer than omega-3

In fact, fatty15 recently went head to head against the most effective, highest performing omega-3 fatty acid supplement, EPA. The results?

Fatty15 was more effective, safer, and better able to help support cellular health than omega-3.*

More Effective

Studies showed that fatty15 had 36 clinically-relevant health benefits.* Omega-3 only had 10. That’s 26 more benefits for your body, including balancing immunity function and maintaining heart health.*


Omega-3s at high doses are toxic to your cells. Out of 12 cell types studied, higher doses of omega-3 killed four of them, including heart and lung cells. Fatty15 was safe for all 12 cell types studied.*

Fatty15, unlike omega-3, is a sturdy fatty acid that can integrate into cell membranes helping protect and support them.* Also important to note: Fatty15 contains only one pure ingredient.

Lastly, you’ll only need 100mg a day of fatty15. That’s enough to increase your circulating level of C15:0 and reap the health benefits of this fatty acid. Compared to the average daily dose of omega-3, which is between 2,000 to 3,000 mg, that’s great news. 

More Cell Support

Fatty15 can help repair and restore our cells. Out of 12 cell types, fatty15 repaired 10 of the 12. Omega-3 was only able to repair 4 of the 12 cell types. In addition, research showed that fatty15 could stop “bad” cells from proliferating.

No fishy stuff

Because fatty15 contains no animal products, including no fish, it does not have the fishy aftertaste or indigestion that is often associated with omega-3. Just the pure, healthy fat your body can use without the fishy stuff. We’re going to go ahead and call that a win. 

Why Can’t I Get Enough C15:0 in My Diet?

C15:0 is primarily found in trace levels in whole-fat dairy products and some types of fish and plants. However, increasing your intake of whole-fat dairy products comes with extra calories, sugars, and high levels of the "bad" even-chain saturated fats.

With fatty15, you can get all the benefits of C15:0, and none of the added calories or sugar you’d get by ingesting a lot of full fat dairy products. 

Fatty15: The Better Fatty Acid 

A fatty acid supplement is a good way to help support your health, but the supplement you’re taking should be safe and effective for your body with minimal side effects. 

Fatty15 is the once-a-day fatty acid supplement, with none of the fishy side effects commonly associated with omega-3, helping to support your health overall. Nothing fishy about it!

Looking to learn more about what C15:0 can do? Explore the science behind fatty15 here


Omega-3 Fatty Acids - Health Professional Fact Sheet | ODS

Omega-3 Supplements: In Depth | NCCIH

Oxidation of Marine Omega-3 Supplements and Human Health | PMC

Profile photo for Eric Venn-Watson

Eric Venn-Watson M.D.

Eric is a physician, U.S. Navy veteran, and Co-founder and COO of Seraphina Therapeutics. Eric served over 25 years as a Navy and Marine Corps physician, working with the special forces community to improve their health and fitness. Seraphina Therapeutics is a health and wellness company dedicated to advancing global health through the discovery of essential fatty acids and micronutrient therapeutics.

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