Potential side effects of taking fish oil supplements include heartburn, nausea, bad breath, loose stools, nosebleeds or rash, according to WebMD. Patients who take fish oil supplements with meals or after freezing them may be able to reduce the prevalence of side effects.
Fish oil supplements are considered to be safe for the majority of the population, as reported by WebMD. The supplement should be taken in only low doses, and patients shouldn't take more than 3 grams of fish oil per day. Doing so may cause a patient's blood to not clot properly and may lead to excessive bleeding.