A small Diff. The xl form lasts longer than the sr. This means it is less likely to make you anxious but it may last long enough to keep you up. I prescribe the xl whenever possible.
Duration of Action. These two forms are relatively equivalent in terms of potential benefit. The primary difference has to do how quickly the medicine is netabolized. The sr form is usually needed twice a day to maintain consistent benefit. The xl form lasts longer, with most people only needing to take it once a day. The xl form tends to have fewer side effect due to a more gradual release into the body.
How long they last. The sr form does not last as long (it is broken down more quickly) so it is usually taken twice daily. The xl form lasts longer so it can usually be taken as a single daily dose in the morning.
Sr vs. xl. Sr is slow release and taken twice daily, xl is extended release taken once daily in am. Also, xl is only brand, sr can come in generic form, cheaper.