One of my sons started having extreme academic problems when he was in high school. We had him tested and the diagnosis came back ADHD.

He began taking a small dose of Ritalin, but it had no effect. They upped it to a moderate dose and he was suddenly able to focus and concentrate in class. It greatly improved his ability to sit in class for 4+ hours and listen and pay attention.

However, he began to notice that, although his in-class focus was greatly improved, as soon as the medication wore off (i,e. late afternoon / early evening), his post-medicated focus and state-of-mind was much worse than it was pre-medicated.

As a result of that realization, he began to search for ways to manage and cope without the meds. He was able to do that and is far happier as a result. (One of the coping methods was getting into a different academic program -- one that was more hands-on and less sitting in a chair listening to lectures).