ELI5 Grapefruit - why no mixing with medications?

What is it about grapefruit that makes it incompatible with so many prescription drugs? What is CYP3A4? What about other similar fruits? Why the name grapefruit if there's no relation to grapes?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: z-freak, smitten430kittens, 2pam, mistmanx, unusually_awkward, zldfn101, iamlizzy1, capt_groomp, dooks4introvert, notyogrannysgrandkid, femifoodie & tgpineapple To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]