Common side effects of fish oil include belching, bad breath, bleeding gums, dizziness and nausea. More severe effects include heartburn, headache, dark brown urine, coughing up blood, loose stool, nose bleeds and rash, according to Drugs.com. Typically these side effects only occur in individuals who take high doses, or more than 3 grams per day.
WebMD classifies fish oil as likely safe for most individuals, including pregnant and breast feeding women, as long as they take low doses (3 grams or less) per day. WebMD also states that taking fish oil pills with food, or freezing the pills first can decrease the side effects.
Those who take high doses of fish oil may not only suffer from the pill’s common side effects, but the oil may reduce the immune system’s ability to fight off infection, meaning elderly individuals, those with HIV or AIDS, and those recovering from major surgery should proceed with caution.
Other individuals with pre-existing medical conditions may be at risk when taking fish oil, including individuals with bipolar disorder, depression and diabetes, as WebMD reveals the oil can increase the symptoms of these conditions. The site also states that too much fish oil can also prevent the blood from clotting and increase the chance of bleeding, particularly in those with liver disease.While fish oil can lower blood pressure, it can cause blood pressure levels to drop too low in those taking blood pressure-lowering medications.