The possible side effects of fish oil pills include belching, bad breath, nausea, heartburn and nosebleeds, according to WebMD. Other side effects include loose stools and rash in some users. Those who take more than the recommended dose of 3 grams per day can suffer from issues with blood clotting.
While side effects with fish oil supplements are typically rare, taking these supplements with meals or freezing the capsules first often decreases common side effects, according to WebMD.
Fish oil supplements are generally safe for most people, including pregnant and breast-feeding women, as long as the supplement is taken in low doses, according to WebMD. Since high amounts of fish oil can reduce the immune system’s activity and ability to fight infection, those taking medications and the elderly should carefully monitor the amount of fish oil they take. With this in mind, those with HIV/AIDS or other immune system compromising conditions should refrain from taking large doses of fish oil supplements.
Individuals with liver disease should proceed with caution, as fish oil may increase the risk of bleeding with those who have liver scarring, states WebMD. Fish oil supplements may increase the symptoms of depression, bipolar disorder and diabetes, and it can lower blood pressure too dramatically in those already taking blood pressure-lowering medications.