Did you know that grapefruit juice is not the best way to wash down certain prescription pills? In simplified terms, grapefruit juice increases the absorption of some medicines, which is sometimes not how they are intended to work, and in rare cases can be life-threatening. These pages go into more detail about the science behind the interactions and also some deaths that have resulted from it. Although I can’t verify all the information presented by that site, there is a list of references at the end.