So far, no evidence has been found of interaction between omega 3 fatty acids and vitamins or drugs. However, if you are taking prescription drugs it would still be wise to inform your physician if you intend to take larger amounts of omega 3 fish oil supplements.
When you buy omega 3 supplements, you should also make sure that the product contains adequate levels of Vitamin E, which acts as stabilizer and that the capsules are packaged individually as a means of protection to light and oxygen.
Also, be aware that cod liver oil and fish oil is not the same. Cod liver oil is very rich in Vitamin A and D, but doesn't contain sufficient amounts of omega 3 fatty acids. If you would try to obtain therapeutic amounts of EPA and DHA from cod liver oil, you would exceed the recommended daily intake of vitamins A and D.
Fish oil on the contrary is very rich in the omega 3 oils EPA and DHA, but contains only little amounts of vitamins A and D. Most producers of omega 3 fish oil supplements add Vitamin E as stabilizer.
