I had an enormous difference between the two. When XR was coming out I read about it and that it was designed for people who needed to be on higher doses but were too sedated. I begged to be allowed to try it immediately and was on it so soon it was hard to find. (This was 2008 I think).

I was able to cut my dose in half and was less sedated. It also just worked better for me and I was then able to wean off Depakote over many months (I was on a ton of it). I lost a great deal of weight (70 lbs I think) and felt much better.

It just didn't last. My antidepressant at the time needed very tight dosing and stopped being effective, leaving me needing an MAOI. When I went on that I had to double my Seroquel XR b/c the MAOI is activating. I still kept the weight off and felt great (even had a regular sleep cycle for the only time in my life although it was odd-11 pm-4 AM daily and that was all the sleep I needed for several years). Eventually my bipolar got a lot worse and my medication needs increased and now I'm on 1200 mg of XR. I don't think there is much difference at this high dose although I don't know for sure. But I gained the weight back and when I'm not manic am pretty sedated (other drugs contribute to this and I need to be somewhat sedated to be ok). However, overall XR was a very positive addition and I'm pretty sure regular release would have just totally stopped working even with the dose being very high.

I still wish I were on less; the days when I was on 600 mg and the MAOI were wonderful.