Doctor Benjamin Carlson is a character in DEXTER. He was a physician assigned to Travis Marshall, who he wrote a psyche evaluation on. According to Carlson, Travis suffered from violent tendencies since childhood, lack of empathy, was a manipulator and had delusions of grander. Carlson even believed that Travis was responsible for the deaths of both of his parents, having grabbed the steering wheel to force their car into a tree killing both of them during his childhood.
Carlson would prescribe a medication known as Chlorpromazine to Travis, which is a form of anti-psychotics. The medication however was not efficient, as Travis eventually killed a man named Professor James Gellar and later became the Doomsday Killer.
Carlson passed away in 2009, of unknown causes. It is likely that Travis still received the prescription medicine or eventually he decided to no longer take it.