Focusyn was an experimental drug created for the purpose of causing Attention Deficit Disorder-inflicted students to cope in class.
It was given to Bart Simpson when it became apparent that he had ADD. Bart was completely reluctant to take the medicine, and it wasn't until Marge guilted him into doing so that he eventually conceded. It had a bit of a delay, as he seemed to still exhibit his usual behavior (such as stuffing oranges in his pants to make it seem as though the medicine caused his testicles to swell), but by the time he got to Mrs. Krabappel's class, the medicine came into effect, shocking the rest of the class about his recent behavior. It also heightened his interest in learning and even his etiquette. However, while it did grant him to use his intellectual potential to the maximum, it also became somewhat apparent that it also affected his sanity somewhat: He became paranoid that the Major League Baseball association was spying on people and doing odd and disturbing behavior. When faced with the possibility of losing Focuslyn, Bart went berserk and, after ingesting several handfuls of Focusyn pills, ran off from the Pharmacist, infiltrated Fort Fragg, and hijacked a Tank with the intention of blowing up the satellite. Because of the incident, Bart was weaned off of Focusyn.
When trying to convince Bart to try some Focusyn, Homer placed some in Taffy in an attempt to trick Bart into ingesting the medicine, and tried ingesting it himself to try and "convince" Bart that it wasn't laced, which caused Homer to wig out, causing their next door neighbors to think that Homer may have been possessed by a demon, and later did it again after Bart took the Focusyn. Whether this was due to a chemical reaction from the combination of Taffy and Focusyn or due to not being legible for the prescription is never specified.
- When Bart became paranoid due to Focusyn's side effects, his facial appearance resembled Hugo Simpson.