Side effects of cod liver oil may include foul breath, belching, nosebleeds and heartburn according to WebMD. Although cod liver oil is most likely safe for most individuals, consuming high doses may lead to an increased risk of bleeding, excess amounts of vitamins A and D, loose stools and nausea.
Cod liver oil, which may be obtained from fresh cod liver or supplements, is used to treat high blood pressure, high triglycerides, high cholesterol, heart disease, depression, middle ear infections and a number of other conditions. However, not all of its uses have been proven effective, according to WebMD. Some people also place cod liver oil in wounds to hasten recovery, but side effects of this usage are unknown. Cod liver oil may interact with certain medications, including anti-hypertensive drugs, which are used for high blood pressure, and anticoagulants, which are used to slow blood clotting.
The Wikipedia entry for cod liver oil states that it possesses higher levels of both vitamin A and vitamin D than fish oil, and it has large amounts of omega-3 fatty acids. Its properties may also help to relieve joint stiffness associated with arthritis. The modern processing procedure for this supplement includes cooking whole cod tissue before removing the oil.