A friend of mine was taking xenadrine and it was making him feel run down. He went to the doctor just to see what was wrong and if he could take it a different way. when the doctor checked him out his heart rate actually slowed down when he took the xenadrine. The doctor told him that in some people who have very fast metabolisms effedrine can actually have a reverse effect. so if you have a naturally fast metabolism maybe thats whats happening to you.