Cod liver oil (the most common form of fish oil) is a very old form of multivitamin (particularly A and D) and fatty acid supplementation. It is found in a large range of over the counter and health shop medications and is available as a cream, capsule and mixture. It is used orally as a tonic and to treat arthritis, and as a moisturiser on the skin.
It is safe in breastfeeding and children, and small amounts are safe in pregnancy, but excess may cause birth defects. The only side effect is its foul taste, but if taken to excess it may cause nausea and diarrhoea.
Its use should cease in patients who have had any acute bleeding illness such as a stroke or bleeding from the bowel, and it should be ceased before any surgery as it may increase the risk of bleeding.