Since so many of us are on Metoprolol, I thought I'd pass on my experience with them. I had been on Metoprolol Tartrate (the non-timed release version of Metoprolol) for a while, taking it twice a day, but was having a lot of problems with insomnia (a common side effect). At various places on the internet I read where some people had less insomnia with the timed-release version (brand name is Toprol XL) of it, so I asked my EP if I could try it, which he said was fine. After a week I started to have a lot of atrial flutter (which I haven't had for a long time). I switched back to the non-timed release version twice a day, and the atrial flutter cut way back. When I saw my EP again today, I told him about this, and he said that some people can react quite differently to the two types of Metoprolol, and this was not unusual.

My point isn't that either type of Metoprolol is better or worse, but that our body can indeed respond differently to them. If you read many posts here it is obvious that different people respond to different meds differently. I just didn't realize a timed-release and a non-timed release of the same drug would fall into this category too.