I'm new to amphetamines, and managed to get an Rx for Adderall. I find it to be good stuff for my supposed ADHD, but am concerned that after 15 mg, my heartrate rises from 75 bpm to 90-110 bpm (considered tachycardia if over 100). I'm going to ask my doctor, but would appreciate input from any experienced users of Adderall or other amphetamines. How serious a sign is tachcardia? Is it possible that it eventually will go away as one's body gets used to the drug?