Why medicines should not be taken with tea?
It has been said that it is not appropriate to take medicine with tea because for example caffeine in tea kills the effect of sleeping pills. It has also been forbidden to take medicine containing iron for the treatment of anemia and it has been advised not to drink tea for 30-60 minutes after taking ferrous pills.
@papiya One of the reasons has been said that considerable amount of catechin (also tannin, 60-70mg of which is contained in a serving of 100ml of Sencha) in tea prevents iron to be absorbed, producing multi-complex. However, VC in green tea promotes the absorption of iron (table1). Recently, it is said not to be that serious because not all iron reacts with catechin. But it is better to avoid tea to take medicine if anemia is caused by lack of iron because it often causes atrophy of mucous membrane of the digestive tract and decreases the secretion of digestive juices, which decreased the absorption rate of iron. Taking medicine with grapefruit juice is said to be a problem these days. The reason is that flavonoids in grapefruit juice prevents the activities of CYP3A4, which is a cytochrom P-450 molecule, and eventually prevents the metabolism of the medicine taken. For example, when taking jihidrobirijin calcium with grapefruit juice, its metabolism is prevented and the density in blood increases, which might cause sub-effects such as lowering blood pressure. In contrast, tea is said to have a selective deriving effect on CYP1 and CYP4 but no sub-effects have been reported.