Fish oil is a blood thinner when taken in high doses, as U.S. News and World Report explains. It interacts with other medications and supplements that thin the blood, including clopidogrel, warfarin, aspirin, ibuprofen and vitamin E.
Because fish oil supplements, whether prescription strength or over-the-counter, can keep blood from clotting, people taking these supplements should let their doctors know, especially if taking nonsteroidal anti-inflammatories regularly or any blood-thinning drugs, as WebMD recommends. Fish oil is especially recommended for patients with heart disease or very high triglycerides. While eating a diet rich in fish and nuts can supply all the omega-3 fatty acids the body needs, taking fish oil supplements helps protect against possible heart disease or pancreatitis.