I think the XR (extended release)is just for seroquel...basically if you are getting it for psychosis you should really be on the XR but if you are getting it for sleep you should be on the IR....

Seroquel is weird it is a very weak D2 antagonist and it will dissociate from the d2 receptor before the day is over if you are using the IR so this is great if you just take it before bed because it will be gone before you wake up if you're just using it for sleep, but if you want the drug to last a full 24 hours and block psychosis you need the XR....otherwise it will just be gone...also there are pretty significant dosing differences between sleep and psychosis too like 50mg vs hundreds...