Limitless is a film where a struggling writer, Eddie Morra, takes a fictional smart drug called NZT-48 that unlocks 100% of his brain, granting him perfect memory, rapid learning, and intense focus, transforming him into a financial success but also attracting dangerous attention. While NZT-48 isn't real, the concept mirrors real-world drugs like modafinil, used off-label as a cognitive enhancer (smart drug) for wakefulness and focus, though it carries risks and isn't a magic bullet for genius like in the movie.