I have been on for about a week now and so far I haven't had any noticeable side effects. But this morning I woke up earlier than usual and my heart was racing and very mild burning sensation in the chest. (I know this is one of the known side effects). It went away after I woke up and got ready. The weird thing is that if its only supposed to be in your system 10-12 hours and I took it almost 21 hours before, its odd that I didn't notice the side effect during the day closer to when I took the pill but only 21 hours later when the effect should have worn off. Has anyone experienced the same thing?