Originally posted by a star
if you want the most from your codeine pain releif, down them with at least 1/2-3/4 litre of yellow grapefruit juice (not ruby red variety) as it comntains an inhibitor of cyctochrome CYP3A4, which is responsible for N-demethylation compounds to their barely active nor compounds (norcodeine & normorphine). I've seen plenty of crap written about it (inhibiting 3A4 doesn't wotk etc), but these tend to come from people who used cimetidine as the 3A4 inhibitor, not realizing that cimetidine is also an inhibitor of CYP2D6, which is the enzyme responsible for O-demethylating codeine to morphine, so no active metabolite formed! (grapefruit juice does work purely as a 3A4 inhibitor, so an increase of plasma morphine does occur.).