"Limitless" is a movie that explores the human cognitive possibilities, and raises the question of how a person would use the power given to them, and what consequences it might entail.
The movie's protagonist is Eddie Morra, an unsuccessful writer who is suffering writer's block and getting dumped from his long-time girlfriend. Eddie suddenly stumbles upon his ex-wife's brother on the street. They have coffee together, and Vernon tells him that he has a solution for his troubles. The solution is a pill that enables the complete usage of the brain. Eddie, knowing that Vernon is a drug dealer, is reluctant but, nevertheless, takes the pill.
Eddie takes the pill and a whole new world opens up to him. He is able to use his abilities to the maximum. He knows what he needs to do and knows how to do it. His book as well is finally finished.
The next day the pill wears off and Eddie visits Vernon for more. After he returns to Vernon's apartment, who sent him on some errand, Eddie discovers Vernon dead. Before the police comes, Eddie finds some cash and a whole bag of the NZT pills.
Eddie uses the pills daily. He grows more and more successful, and meets important people among who is Carl Van Loon, a businessman involved with the stock market. They partner up, and Eddie is hopeful for his future. He even gets back together with Lindy.
Eddie soon starts to feel the side effects of the pill. He loses hours of his days, not knowing what he was doing. The guy who loaned him money wants it back, and in one of their confrontations, the criminal called Gennady takes the pill as well. He starts demanding a supply from Eddie. Eddie notices that he's being followed by a man in a tan suit, who later attacks Lindy while she is on the way to get him the pills.
Eddie has a conversation with his ex-wife Melissa as well, who reveals that all the people who've been taking the pills suffered horrible consequences. They aren't able to use their strength and abilities to function normally are damaged. Melissa is one of those people. He decides to use the pills more cautiously.
Van Loon and Eddie set up a meeting with a businessman called Atwood. Atwood fails to join the signing of the important contract between them because he falls ill. Eddie discovers that Atwood is one of the people who've been taking the pill as well, and is now suffering the consequences. Atwood dies, and Eddie discovers that the man in the tan coat is his worker.
Eddie returns to his apartment after realizing that someone pocketed his pills and sent him a package containing severed hands of his bodyguards. Gennady and his men come there demanding more of the pills, and try to kill him. Eddie retaliates and kills them. He meets with the man in the tan coat who gives him the supply of the pills.
The movie's ending scene is Eddie in the future. He became a senator. He receives a visit by Van Loon, who demands from Eddie to work for him, threatening him with the knowledge about the pills. Eddie reveals that he no longer uses them. He discovered a way to use their benefits without the side effects. Defeated, Van Loon gets back into his car, and Eddie goes to have dinner with Lindy.
