Bleeding

Fish oil can have some hazardous adverse effects, one of which is that it can prevent your blood from clotting. Two of the most noticeable adverse effects are nosebleeds and bleeding gums.

One study of 56 participants showed that giving healthy adults 640 mg of fish oil daily for four weeks reduced blood clotting. Another small study revealed that consuming fish oil may increase the risk of nosebleeds, noting that 72% of adolescents consuming 1 to 5 grams of fish oil daily reported nosebleeds as a side effect. This is why it's often advised to stop taking fish oil before surgery and consult your doctor if you're on blood thinners like Warfarin before taking supplements. Additionally, fish oil can cause significant blood loss and gastrointestinal bleeding when consumed in large amounts. You might also have brain bleeding that results in a hemorrhagic stroke.