EPA and DHA are the components that actually do you good. its likely that fish oil and cod liver oil tablets contain different amounts. it doesn't matter how many mg the actual tablets are, but you need about 450mg of EPA and DHA combined per day. If, like me, you don't eat any fish you'll need this all to come out of the tablets. Most of the ones sold at Tesco, Boots etc are cheap and don't come near to this amount. I get mine from Holland and Barratt, they are about twice the price but contain the right amount of EPA and DHA.