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Side Effects of Omega-3 Fatty Acids

Heartburn, indigestion, and diarrhea are some of the potential side effects of omega-3 fatty acids. Fish oil products may cause a fishy aftertaste or bad breath, while flaxseed or flaxseed oil may cause constipation or bloating. Some omega-3 fatty acid side effects are more serious and should be reported to a healthcare provider, including signs of bleeding, high blood sugar, or allergic reactions.

Do Omega-3 Fatty Acids Cause Side Effects?

A normal dietary intake of omega-3 fatty acids (through food) is probably free of significant side effects. However, even though they are "natural" products, omega-3 supplements may cause side effects. For most people, these side effects are merely bothersome. However, omega-3 fatty acids can sometimes cause serious side effects as well, especially when taken at higher dosages (which is often necessary in order to obtain some of the benefits of omega-3).

Serious Side Effects of Omega-3 Fatty Acids

There are a number of side effects with omega-3 fatty acids that you should report to your healthcare provider and which may indicate that you should stop taking omega-3. These include, but are not limited to:
  • Any signs of bleeding (which may theoretically occur with high doses of omega-3 fatty acids), such as:
    • Easy bruising or bleeding
    • Black, tarry stools; bright red blood in the stool; or vomiting of blood (signs of gastrointestinal bleeding)
    • Signs of a hemorrhagic stroke (bleeding in the brain), such as vision or speech changes, weakness or numbness in an arm or leg, or a severe headache
  • High blood sugar (hyperglycemia), usually in people who already have diabetes
  • Signs of an allergic reaction, such as:
    • An unexplained rash
    • Hives
    • Itching
    • Unexplained swelling
    • Wheezing
    • Difficulty breathing or swallowing.
Some omega-3 fatty acids (the ones found in fish oil) can also increase LDL cholesterol ("bad" cholesterol). Of course, dangerous side effects are possible if a fish oil omega-3 supplement contains heavy metals or other toxins, some of which may be carcinogenic (may increase the risk of cancer). This is why it is important to choose a fish oil supplement that has been adequately purified and tested for toxins.
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Information on Omega-3 Fatty Acids

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