Just to throw my two cents in. I was on Vyvanse but it wasn't working for me (newly diagnosed ADD), it helped a little at first but after a couple weeks it wasn't doing anything. So my doc started me on Adderall XR 20 mg. She said to take one for a few days and if that didn't help to try two 20mgs. Whether I took one (which didn't help enough) or two (first day today, taking two) I have had a rapid heartbeat like my chest is pounding. I have just assumed it was normal considering this is a stimulant I am taking and my body isn't used to it yet. If it continues then I'll contact my dr. But the 2 seems to be helping today. I'm able to focus and get my work done!