Fish Oil

The Side Effects of Fish Oil Supplements

Is It Safe to Take Fish Oil Before Surgery & Medical Procedures?

For years, doctors have advised patients to stop taking fish oil before surgery. Because omega-3 fish oil and cod liver oils have a noted blood thinning effect, it was long believed that consuming these kinds of oils could increase a patient’s risk of bleeding during an operation.

New studies, however, have extensively documented that taking omega-3 supplements before operations not only appears to be safe, but may even be highly beneficial.

So what does that mean for patients and their recovery?

Is Fish Oil Before Surgery Really a Risk?

The efforts to analyze the hypothetical bleeding risk of omega-3s have been ongoing for years. In 2007, Dr. William Harris, PhD (co-inventor of the omega-3 index) reviewed 19 clinical studies involving more than 4,000 surgical patients. These patients took fish oil supplements at doses ranging from 1.6 to 21g of EPA/DHA per day. In the studies analyzed, the patients also took aspirin or heparin — two common blood-thinning drugs.

The review concluded that the risk of problematic bleeding was virtually nonexistent, even when combined with other medications known to increase the risk of bleeding (1).

Another review from 2008 similarly found that no published studies had reported clinically significant bleeding episodes among patients treated with antiplatelet drugs and fish oil at doses ranging from 3 to 7g every day (2).

Even Large Amounts of Omega-3s Considered Safe

More recent studies have added to the evidence. One review from 2018 found it safe to consume doses of up to 10g of EPA/DHA per day in the short-term (3). For context, that would be the same as swallowing almost ¼ cup of Omega Cure® fish oil, or taking 33 regular fish oil capsules daily, which is significantly more omega-3 than any patient needs to take.

Similarly, another 2017 study focused on children, also declared that fish oil therapy surrounding surgery was safe and did not increase the risk of bleeding (4).

There’s little evidence to support the need to stop an omega-3 regimen before surgery. On the flip side, research suggests fish oil could have benefits for patients before and after operations.

Benefits of Fish Oil Before and After Surgery

In the medical community today, there’s excitement that omega-3 fatty acids may actually reduce the risk of infections and complications post-surgery. In addition, studies indicate that omega-3s could potentially improve microbiome health, regulate constipation, ease anxiety, and reduce the need for excessive painkillers – all common concerns for surgical patients.

1. Fewer Post-Surgical Infections

One review analyzed the effects of omega-3 supplementation on pre- and post-surgery colon cancer patients. These types of operations are especially risky due to the high occurrence of postoperative infections. The authors found that omega-3 supplementation was associated with fewer post-surgical infections, as well as a shorter hospital stay (5).

2. Reduced Risk of Cardiac Complications

In a 2017 review, another group of researchers similarly discovered that omega-3 supplementation reduced the length of hospital stays, as well as the risk of atrial fibrillation (6).

A 2018 study co-authored by Dr. William Harris also investigated the risk of bleeding during cardiac surgeries. During the week before their scheduled surgeries, more than 1500 patients were randomly assigned to take either a placebo or 6.5 to 8g of EPA/DHA. Starting from the day of their surgery until their release from hospital, the omega-3 group continued to take 1.7g of EPA/DHA.

The results? The team discovered that patients with higher EPA/DHA blood levels actually had a lower risk of bleeding and saw a reduction in the number of blood transfusions (7).

3. Improved Microbial Health

In recent years, researchers have also started to look at the microbiome’s influence on the immune system. The microbiome — the name used to describe the bacteria that live in and on us — can either support or hurt our health, depending on the composition and types of germs.

During surgery, patients are typically both exposed to new types of bacteria and are also given antibiotics that kill off many existing microbial team-players. Both of these factors can disrupt the microbiome, which is why it is important to help support the good bacteria as best as possible.

Studies show that omega-3 fatty acids improve the ratio of beneficial to harmful bacteria, as well as diminish the ability of harmful bacteria to colonize the stomach (8, 9). In addition, fish oil also diminishes the amount of pro-inflammatory endotoxins produced by harmful bacteria (10). All of these benefits can potentially make a big difference for patients’ vulnerable immune systems in a hospital setting.

The research surrounding the microbiome is changing our understanding of disease prevention today. While many factors contribute to microbial health, the types of nutrients we consume — including omega-3 fatty acids — make a big difference.

4. Regulating Post-Surgery Constipation

Studies also show that omega-3 fish oil intake is also useful in avoiding one of the biggest post-surgical complications: constipation. Regaining intestinal tract function after surgery can be difficult due to pain medication (especially opioids), diuretics, muscle relaxants, anesthesia, and lengthy bed rest. Using fish oil, however, can help to lubricate the intestinal tract, allowing for easier bowel movements.

Dr. William Kennedy – a leading US orthopedic surgeon – explains that constipation often results in rising body temperatures, leading many overseeing physicians to believe that their patient is experiencing an infection. In this situation, patients are often prescribed unnecessary antibiotics when a bowel movement could be the simplest solution.

5. Eased Effects of Anxiety

Prior to surgery, it’s common to feel increased anxiety and fear, and more research suggests that omega-3s can help manage some of the emotional stress.

In a 2018 meta-analysis, researchers demonstrated a connection between omega-3s and lowered anxiety in patients with a clinical diagnosis — with the caveat that the patients needed an effective omega-3 dose to get results (11).

Further studies also suggests that omega-3s can be beneficial when coping with other instances of stress, like having an acute myocardial infarction, post traumatic stress disorder (PTSD), or even a stressful exam (11). While more clinical studies need to be done with larger sample sizes, these initial findings are promising.

6. Managing Pain and Inflammation

Recovering from surgery is typically a long and painful process, even under the best conditions. But when a person does not get enough omega-3s, they may be putting themselves at risk for extending that process.

Having a high omega-6 to omega-3 ratio is strongly associated with chronic inflammation and pain (12, 13). Furthermore, studies indicate that when patients receive a sufficient daily dose of omega-3 fish oil, it tends to limit their need for painkillers.

Support Your Health with Fresh Fish Oil

It’s time to rethink the old approach of stopping to take omega-3 supplements prior to surgery. Nobody tells patients to stop eating fish. And as the above research demonstrates, consuming omega-3s from fish oil prior to surgery is similarly safe, unless a person has a bleeding disorder or is on lots of blood thinning medications. In addition, data suggests that getting an effective omega-3 dose can make a difference on you road to recovery.

For patients and practitioners thinking about omega-3 supplementation, however, it is crucial to consider the dose and quality of the oil. For more on that, read “Fresh Fish Oil: Why It Matters to Your Health.”

An Effective Omega-3 Dose, Made Simple Experience the Omega3 Innovations difference for yourself with the most effective fish oil supplement on the market. Buy Now


1. Harris, W.S. (2007). Expert Opinion: Omega-3 fatty acids and bleeding—Cause for concern? Report of the National Lipid Association’s Safety Task Force: The Nonstatins. American Journal of Cardiology, 99.6A: 44C-6C.

2. Braun, L. (2013). Fish Oils and Bleeding: ‘Is There a Clinically Significant Risk? BioCeuticals.

3. Jeansen, S., Witkamp, R.F., Garthoff, J.A., van Helvoort, A., and Calder, P.C. (2018). Fish Oil LC-PUFAs Do Not Affect Blood Coagulation Parameters and Bleeding Manifestations: Analysis of 8 Clinical Studies with Selected Patient Groups on Omega-3-Enriched Medical Nutrition. Clinical Nutrition, 37(3):948-957.

4. Nandivada, P. et al. (2017). Risk of Post-Procedural Bleeding in Children on Intravenous Fish Oil. American Journal of Surgery, 214(4):733-737.

5. Xie, H., and Chang, Y. (2016). Omega-3 Polyunsaturated Fatty Acids in the Prevention of Postoperative Complications in Colorectal Cancer: A Meta-Analysis. OncoTargets and Therapy, 9: 7435–7443.

6. Langlois, P.L., Hardy, G., and Manzanares, W. (2017). Omega-3 Polyunsaturated Fatty Acids in Cardiac Surgery Patients: An Updated Systematic Review and Meta-Analysis. Clinical Nutrition, 36(3):737-746.

7. Akintoye, E., Sethi, P., Harris, W.S., et al. (2018). Fish Oil and Perioperative Bleeding. Circulation: Cardiovascular Quality and Outcomes, 11(11):e004584.

8. Correia, M. et al. (2012). Docosahexaenoic Acid Inhibits Helicobacter Pylori Growth In Vitro and Mice Gastric Mucosa Colonization. PloS One, 7(4), e35072.

9. Kim, Y. G., Lee, J. H., Raorane, C. J., Oh, S. T., Park, J. G., and Lee, J. (2018). Herring Oil and Omega Fatty Acids Inhibit Staphylococcus aureus Biofilm Formation and Virulence. Frontiers in Microbiology, 9, 1241.

10. Kaliannan, K. et al. (2015). A Host-Microbiome Interaction Mediates the Opposing Effects of Omega-6 and Omega-3 Fatty Acids on Metabolic Endotoxemia. Scientific Reports, 5, 11276.

11. Su, K. P., Tseng, P. T., Lin, P. Y., Okubo, R., Chen, T. Y., Chen, Y. W., and Matsuoka, Y. J. (2018). Association of Use of Omega-3 Polyunsaturated Fatty Acids With Changes in Severity of Anxiety Symptoms: A Systematic Review and Meta-Analysis. JAMA Network Open, 1(5), e182327.

12. Sibille, K. T. et al. (2018). Omega-6: Omega-3 PUFA Ratio, Pain, Functioning, and Distress in Adults With Knee Pain. The Clinical Journal of Pain, 34(2), 182–189.

13. DiNicolantonio, J. J., and O’Keefe, J. H. (2018). Importance of Maintaining a Low Omega-6/Omega-3 Ratio for Reducing Inflammation. Open Heart, 5(2), e000946.

Fish Oil, Omega-3 Fatty Acids Capsules (OTC)

What is this medication?

FISH OIL, OMEGA-3 FATTY ACIDS (fish oyl, oh MEH guh three FA tee A suhds) support heart, brain, and eye health. They may also decrease inflammation. Omega-3 fatty acids are essential fats the body needs to support overall health. This supplement is not intended to diagnose, treat, cure, or prevent any disease.

This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions.

COMMON BRAND NAME(S): Omega MonoPure EPA, Omega-3, Omega-3 Fish Oil, OmegaPure 780, OmegaPure 900, TherOmega, THEROMEGA SPORT

What should I tell my care team before I take this medication?

They need to know if you have any of these conditions

Bleeding problems

Lung or breathing disease, like asthma

An unusual or allergic reaction to fish oil, omega-3 fatty acids, fish, other medications, foods, dyes, or preservatives

Pregnant or trying to get pregnant


How should I use this medication?

Take this medication by mouth with a glass of water. Follow the directions on the package or prescription label. Take with food. Take your medication at regular intervals. Do not take your medication more often than directed.

Talk to your care team about the use of this medication in children. Special care may be needed. This medication should not be used in children without a care team's advice.

Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once.

NOTE: This medicine is only for you. Do not share this medicine with others.

What if I miss a dose?

If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses.

What may interact with this medication?

Aspirin and aspirin-like medications

Herbal products like danshen, dong quai, garlic pills, ginger, ginkgo biloba, horse chestnut, willow bark, and others

Medications that treat or prevent blood clots like enoxaparin, heparin, warfarin

This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.

What should I watch for while using this medication?

Follow a good diet and exercise plan. Taking a dietary supplement does not replace a healthy lifestyle. Some foods that have omega-3 fatty acids naturally are fatty fish like albacore tuna, halibut, herring, mackerel, lake trout, salmon, and sardines.

Too much of this medication can be unsafe. Talk to your care team about how much of this medication is right for you.

If you are scheduled for any medical or dental procedure, tell your care team that you are taking this medication. You may need to stop taking this medication before the procedure.

Herbal or dietary supplements are not regulated like medications. Rigid quality control standards are not required for dietary supplements. The purity and strength of these products can vary. The safety and effect of this dietary supplement for a certain disease or illness is not well known. This product is not intended to diagnose, treat, cure or prevent any disease.

The Food and Drug Administration suggests the following to help consumers protect themselves:

Always read product labels and follow directions.

Natural does not mean a product is safe for humans to take.

Look for products that include USP after the ingredient name. This means that the manufacturer followed the standards of the US Pharmacopoeia.

Products made or sold by a nationally known food or drug company are more likely to be made under tight controls. You can write to the company for more information about how the product was made.

What side effects may I notice from receiving this medication?

Side effects that you should report to your care team as soon as possible:

Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat

Side effects that usually do not require medical attention (report to your care team if they continue or are bothersome):

Bad breath


Fishy aftertaste


Upset stomach

This list may not describe all possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Where should I keep my medication?

Keep out of the reach of children.

Store at room temperature or as directed on the package label. Protect from moisture. Do not freeze. Throw away any unused medication after the expiration date.

NOTE: This sheet is a summary. It may not cover all possible information. If you have questions about this medicine, talk to your doctor, pharmacist, or health care provider.

The Side Effects of Fish Oil Supplements

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.

: 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.

: 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:




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.

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


Hypoglycemia (high blood sugar)

Hypotension (low blood pressure)


Acid reflux


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.

Eric Carter