Cod-Liver Oil: This supplement is extracted from the liver of the Cod fish. It's high levels of omega-3 (fatty acids) are very high with Vitamin A, D  and E. 

Some of it's beneficial uses are for arthritic joint  pain.

Below is a short list of it's medicinal benifits:
creates healthy benifits for your heart
bone health
brain health
skin health
hair health
nail health
minor burns
assists in the treatment of multiple sclerosis
lowers the risk of diabetes in prenatal care (infants)
increases nutrient of mother breat milk (fatty acids)
prevention in infection

Adverse  Side effects: Humans can take too much Vitamin A ( as the body does not assimilate the vitamin readily) and it does store it in the fat tissues of humans, creating a harmful levels.  Pregnant women can benifit with Vitamin A but caution should be taken when pregnant, as birth deffects have been blamed on high consumption of Vitamin A.