Side Effects Of Fish Oil

Side Effects Of Fish Oil

Fish oil is a healthy substance that comes from the oils of fatty fish or from fish oil supplements. It contains omega-3 fatty acids, mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which confer many health benefits, as shown by many clinical trials.

Fish oil is considered generally safe for children and adults, including pregnant and lactating women. The American Heart Association (AHA) recommends the consumption of 1 gram of fish oil in the diet in the form of oily fish (3.5 ounces) at least twice a week. The International Society for the Study of Fatty Acids and Lipids recommends a minimum intake of 500 mg EPA+DHA for adults and 300 mg DHA daily for pregnant and lactating women. Taking low doses of fish oil (up to 3 grams) is considered to be within safe limits. However, like many substances, improper intake or sensitivity to it may bring about undesirable side effects.

Common Minor Side Effects

Most people experience few or no side effects when taking fish oil supplements. Common, undesirable but minor side effects of fish oil include gastrointestinal disturbances like belching, bad (fishy) breath, fishy aftertaste, nausea, heartburn or indigestion, and loose stools or diarrhea. These effects may be more pronounced as increasing dosages are taken.

Some people complain of having oily skin when taking fish oil. This can sometimes cause acne, although the body may also stop producing extra oil of its own and prevent acne.

Serious Side Effects

Serious adverse reactions may occur when fish oil is taken in large doses regularly. These include:

  • Increased the risk of bleeding – This is due to thinning of the blood which prevents clotting. This can result in gastrointestinal bleeding which may be manifested as dark, tarry stools, bright red blood in the stool or vomiting of blood. One can also experience easy bruising or bleeding, nosebleeds, dizziness, and low blood pressure.
  • Increased risk for stroke – This is related to the increased bleeding tendency which may occur in the brain, resulting in severe headache, weakness of one side of the body and changes in vision or speech.
  • High blood sugar (hyperglycemia), usually in people who are diabetic
  • In people with HIV or compromised immune system higher doses of fish oil can lower the body’s immune system responses.
  • Fish oil may contain traces of mercury and other environmental toxins. These are harmless in small doses, but if taken in excess, serious health problems may arise.
  • A few people who are allergic to fish and seafood may also be allergic to fish oil supplements. Signs and symptoms of an allergic reaction include an unexplained rash, itching, hives, unexplained swelling of the face, wheezing and difficulty in breathing or swallowing.
  • Taking large amounts of fish oil may increase the symptoms of depression and bipolar disorder.

Drug Interactions

The effects of some medications may be reduced or increased when taking large doses of fish oil supplements. On the other hand, the beneficial effects of fish oil may also be reversed by the intake of other medications.

  • Birth control pills or contraceptive drugs might decrease the effectiveness of fish oil.
  • Taking fish oils along with antihypertensive drugs (medications for high blood pressure) might cause the blood pressure to go too low.
  • Orlistat (Xenical) is a weight loss drug which might decrease the absorption of fish oil when they are taken together. To avoid this potential interaction these medications must be taken at least 2 hours apart.
  • Anticoagulant / antiplatelet drugs are medications that slow blood clotting. Taking fish oil along with these may increase the chances of bleeding.


Fish oil supplements provide many health benefits that have been demonstrated by clinical trials. Recommendations on dosages for their specific use in preventing or treating some conditions are based on studies, and these must be carefully followed to avoid any untoward side effects. Most side effects occur as result of taking excessive doses of fish oil, and these can be avoided by getting proper medical advice prior to their use.


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  4. eMouse, M. Fish Oil Side Effects: The Good and the Bad. Health Guidance.