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. This includes:

  • Fatty fish: The AHA suggests consuming two servings of fatty fish (such as salmon, anchovy, herring, and tuna) per week.
  • Nuts: A small handful of 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 take anti-platelet drugs like Plavix (clopidogrel) or anticoagulants like Coumadin (warfarin). Taking these drugs with high-dose omega-3 supplements can increase the risk of bleeding or easy bruising.

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.

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 healthcare provider 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
  • Hyperglycemia (high blood sugar)
  • Hypotension (low blood pressure)
  • Diarrhea
  • Acid reflux
  • Insomnia

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 the 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.

Correction - February 2, 2023: This article was updated to clarify that high blood sugar is hyperglycemia.

8 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. Abdelhamid AS, Brown TJ, Brainard JS, et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2018 Jul 18;7(7):CD003177. doi:10.1002/14651858.CD003177.pub3

  2. Office of Dietary Supplements. Omega-3 fatty acids: fact sheet for health professionals.

  3. American Heart Association. Fish and omega-3 fatty acids.

  4. Novotny K, Fritz K, Parmar M. Omega-3 fatty acids. In: StatPearls [Internet].

  5. Chen C, Yu X, Shao S. Effects of omega-3 fatty acid supplementation on glucose control and lipid levels in type 2 diabetes: a meta-analysis. PLoS One. 2015;10(10):e0139565. doi:10.1371/journal.pone.0139565

  6. Akintoye E, Sethi P, Harris WS, et al. Fish oil and peri-operative bleeding: insights from the Omega-3 Fatty Acids for Prevention of Postoperative Atrial Fibrillation (OPERA) Randomized Trial. Circ Cardiovasc Qual Outcomes. 2018 Nov;11(11):e004584. doi:10.1161/CIRCOUTCOMES.118.004584

  7. Hamazaki T, Colleran H, Hamazaki K, Matsuoka Y, Itomura M, Hibbein J. The safety of fish oils for those whose risk of injury is high. Military Med. 2014:179(11):134. doi:10.7205/MILMED-D-14-00157

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By Jennifer Moll, PharmD
Jennifer Moll, MS, PharmD, is a pharmacist actively involved in educating patients about the importance of heart disease prevention.