It is only 18mg. I used to take this dosage when I was in elementary school but we stopped due to the negative side effects. Now that I am in college we decided to try it again and today is the first day. It has been about an hour and I haven't noticed anything. I think this may be because I am 3 times as heavy as I was when I was 7 years old. Does it take weeks to work? Do I need a higher dose? It used to work great but that was years ago. Any help would be great.