A physician called our pharmacy today asking us about the difference between Wellbutrin SR and Wellbutrin XL. The pharmacist told him that the main difference was that XL was typically prescribed only once daily versus twice daily for the SR. I'm often confused about the XL's and the SR's of the pharmacy world so I did some research to clarify the difference between these two. It looks like SR is approved for smoking cessation and XL is not. Also, it lists XL as being approved for Seasonal Affective Disorder, but not SR. Are these differences in approval just due to the fact that studies were done for the specific dosage form and perhaps not on the other? It seems to me that if XL would work for a disorder that SR would probably also work for that disorder, but that maybe noone has done a study to prove that specifically. What are the side effect profiles like? I would think they are most likely similar, but maybe since the SR is often split into twice daily dosing it has slightly less SE's? Anyone know any other specifics on the differences between these two drugs? Would you recommend one over the other?