I may be wrong, but I think most lactose-free milk is ultra-pasteurized because that disables the lactose, so that it cannot react with lactase enzymes.

And, we keep milk 2-3 max past its expiration date. As for the drugs... some drugs (fortunately not very many) DO go bad after their expiration dead... tetracycline can become very dangerous and things like hydrogen peroxide lose effectiveness with light and over time, thus why it is stored in a dark brown bottle.