I took 500 mg once the first day and then twice the next day. The second night I woke up in a sweat, my heart was racing and had an irregular beat. I am not taking this anymore. I called my doctor(actually a FNP) and left a message but she has not called bacl yet. I then asked the pharmacist and he said that would be VERY RARE, but I should stop taking it until I talk to my doctor.