I tend to be given the same brand of levo each month as I stick to the same pharmacy and so far they have worked very well. However recently I was given a different brand, can't remember the name as I threw them out eventually. I felt so ill, my bp went up and my gp told me rest completely. I suddenly realised that the symptoms had come on after starting the new tablets so I got a new prescription and made sure I got my old brand. Very quickly things improved and I'm now back to normal. When I mentioned it to my GP on my next check up, he said although the ingredients should always be the same, it has been known for cheaper brands to affect people. Has anyone else experienced this?