Fish oil is usually well-tolerated and safe. Common side effects from taking fish oil supplements include stomach pain, fishy breath and burps, heartburn, nausea, and diarrhea. Also, some fish oil formulations have been linked to increased levels of low-density lipoprotein (LDL) cholesterol. Fish oil supplements are not strictly regulated, and some may contain contaminants, oxidized fatty acids, saturated fats, and other impurities that may reduce the overall benefit of the supplement. Fish oil has antiplatelet effects, although most clinical research has not found that supplementation with fish oil increased bleeding risk. A large 5-year study in Japan did find a small increase in bleeding in people taking prescription eicosapentaenoic acid (EPA), though.[1]
What are fish oil’s main drawbacks?
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•Last Updated: May 16, 2025
Fish oil supplements are generally safe but can cause side effects such as stomach pain, fishy breath, and diarrhea, and some formulations may raise LDL cholesterol levels or contain contaminants. Additionally, although most studies show no increased bleeding risk, one study did find a slight increase in bleeding among participants who were taking prescription EPA.