Side Effects of Fish Oil Supplements

Fish oil capsules, walnuts, chia seeds, salmon, and almonds

Verywell / Anastasia Tretiak

Omega-3 fatty acids are a type of polyunsaturated fat found in high concentrations in certain fish, vegetables, nuts, and seeds. These include eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA), each of which is known to offer a variety of health benefits.

Omega-3 fatty acids seem particularly useful in preventing atherosclerosis and heart disease. Studies have shown that consuming between 2 grams and 4 grams of omega-3 fatty acids per day can lower your triglyceride levels by anywhere between 20% and 45%.


The American Heart Association (AHA) recommends consuming obtaining omega-3 fats from foods, such as:

  • Fatty fish: The AHA suggests consuming two servings of fatty fish (such as salmon, anchovy, herring, and tuna) per week.
  • Nuts: Studies have shown that a handful of nuts: such as walnuts, pecans, or almonds: can have a positive impact on your lipid profile.
  • Seeds: Chia and flax are rich sources of omega-3s.

However, if you don't like fatty fish, nuts, or seeds, you can try fish oil supplements instead. They readily available over the counter in softgel capsule form.

Possible Side Effects

Although fish oil may seem like an easy way to improve your heart health, there are side effects associated with its use These appear to be dose-dependent, meaning that the higher dose you take, the more likely you will be to experience side effects.

The most common side effects include:

  • Nausea
  • Diarrhea
  • Heartburn
  • Abdominal pain
  • Belching a fish-like aftertaste

Taking high doses of omega-3 fats, including those found in fish oil supplements, may interact with certain medications. This especially holds true if you have diabetes are taking anticoagulant ("blood thinners").

Additionally, high doses of omega-3s found in fish oil may slightly increase your blood sugar levels. In most cases, the effect won't interfere with diabetes medication or increase your risk of diabetes. Still, if you are struggling to manage your blood sugar, fish oil may not be the best option for you.

Omega-3 fatty acids can also slow blood clotting. Doing so can amplify the effects of anticoagulants like Coumadin (warfarin) or Plavix (clopidogrel), increasing the risk of easy bleeding or bruising.

You should avoid taking fish oil supplements at least a week before scheduled surgery (including dental surgery) to prevent excessive bleeding.

To avoid interaction, always advise your doctor about any medications you are taking, whether they are prescription, over-the-counter, dietary, herbal, or recreational.

Fish oil capsules

Verywell / Anastasia Tretiak


People with heart disease are often advised to take 1 gram (1,000 milligrams) of a combination of DHA and EPA from fish oil each day.

As beneficial as fish oil may be, It is possible to overdose on omega-3 fatty acids, triggering an array of adverse events, including:

  • Bleeding gums
  • Nosebleeds
  • Hypoglycemia (high blood sugar)
  • Hypotension (low blood pressure)
  • Diarrhea
  • Acid reflux
  • Insomnia
  • Vitamin A toxicity

Doses of omega-3 fatty acids greater than 3 grams (3,000 milligrams) may increase your risk of bleeding, even if you are not taking blood-thinning medications.

There is also concern that high intake of omega-3 fatty acids could slow blood clotting to such a degree as to increase the risk of hemorrhagic stroke. People at risk of stroke should only use fish oil under the supervision of a cardiologist.

Because fish oil contains high amounts of vitamin A, it is possible to develop vitamin A toxicity by taking too much. Symptoms include dizziness, nausea, joint pain, and skin irritation.

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Office of Dietary Supplements/National Institutes of Health. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. Bethesda, Maryland; updated July 9. 2019.

Additional Reading
  • Dipiro JT, Talbert RL. Pharmacotherapy: A Pathophysiological Approach, 9th ed 2014.
  • Micromedex 2.0.  Truven Health Analytics, Inc. Greenwood Village, CO.