Possible side effects of omega-3 fish oils containing DHA and EPA may include fishy aftertaste, nausea, bloating and burping, according to WebMD. More serious side effects, such as bleeding, bruising or an allergic reaction, may also occur. A doctor should be notified if these side effects persist.
Fish oil supplements are likely safe in doses less than 3 grams, as reported by WebMD. Doses between 2 grams and 5.4 grams were tolerated during clinical trials, says Drugs.com. High doses of the substance may reduce immune system activity, keep blood from clotting and increase instances of bleeding. Normal doses may cause heartburn, loose stools, rashes and nosebleeds. Consuming large amounts of fish oil from dietary sources may be unsafe due to high mercury levels in fish. Fish oil supplements usually do not contain contaminants.
Omega-3 fish oil products are considered safe for consumption for up to 3.5 years, according to Mayo Clinic. Fish oil supplements may increase DHA levels in newborns if the supplement is ingested during pregnancy. Omega-3 supplements may affect blood sugar levels, so patients with diabetes or hypoglycemia should use caution when taking these supplements. Fish oil can lower blood pressure, affect cholesterol levels and cause vitamin E.