Mental Health Home > Side Effects of Docosahexaenoic Acid

Gas, nausea, and a fishy aftertaste are common side effects of docosahexaenoic acid. Since the supplement may have anticoagulant effects, some people may bruise more easily, and it may take longer for a cut to stop bleeding. Some docosahexaenoic acid side effects (such as vomiting of blood) may indicate that you should stop treatment.

Does Docosahexaenoic Acid Cause Side Effects?

Even though it is a "natural" product, docosahexaenoic acid (DHA) is not always free of side effects. For most people, these side effects are merely bothersome. However, docosahexaenoic acid can sometimes cause serious side effects as well, especially when taken at higher dosages. Also, it is possible that docosahexaenoic acid obtained from fish sources could contain heavy metals or other toxins, if it is not purified properly.

Serious Side Effects With Docosahexaenoic Acid

There are a few side effects with docosahexaenoic acid that you should report to your healthcare provider and which may indicate that you should stop taking docosahexaenoic acid. These include, but are not limited to:
  • Signs of internal bleeding, such as:


    • 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


  • Signs of an allergic reaction, including an unexplained rash, hives, itching, unexplained swelling, wheezing, or difficulty breathing or swallowing.
Docosahexaenoic acid may also slightly increase LDL cholesterol ("bad cholesterol"). Of course, dangerous side effects are possible if a docosahexaenoic acid supplement contains heavy metals or other toxins, some of which may be carcinogenic (may increase the risk of cancer). This is most likely in docosahexaenoic acid supplements derived from fish, especially if not purified.
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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