Plot

Justin throws himself and everyone around him into chaos when he attempts to break free from his addiction to his thumb.

Justin is a teenager boy, who has an oral obsession with his thumb. His mother seems to be a normal housekeeper, but she has her own obsessions as well, like a crush on a TV-star. The only person who's aware of Justin's problem is his father, manager in a store, but none of his advices seem to be working for Justin. The kid is signed up in a debate workshop, but the thing isn't going well, because he has his mind in a pretty classmate and, of course, in his thumb, affecting all the rest of his classes. So, Justin is a loner kid in the school, who prefers to lock himself in the bathroom and suck his thumb. Justin's dentist, a mystical-hippie person, will try to help to overcome his thumb problem, through the hypnosis. But the school's psychologist will diagnose Justin with the Attention Deficit Disorder, and will prescribe him some drugs. Suddenly, Justin's problem with his thumb will disappear, becoming an hyperactive genius, winning several debate contests and the admiration from his teacher. Nevertheless, more serious problems will come for Justin with his mother, his father and with a drug addiction.—Alejandro Frias

Justin Cobb (Lou Taylor Pucci) is a shy 17-year-old in a family of four in suburban Oregon. He has a persistent thumb-sucking habit his father Mike (Vincent D'Onofrio) disapproves of, which has led to major orthodontic repair. He addresses his parents by their first names, Mike and Audrey, so as not to make his father feel old. Cobbs are a normal middle-class family and live a normal life. Mike is the manager of a sports retail store. Audrey (Tilda Swinton), a registered nurse, is idly fascinated by actor Matt Schramm (Benjamin Bratt), entering a contest to win a date with him in New York. She insists it is "innocent fun" but is inordinately concerned with looking attractive for the contest. Audrey has to write about her most distinctive feature to win the contest.

Justin struggles on his school's debate team, led by Mr. Geary (Vince Vaughn), which he joined to get closer to his environmentalist classmate Rebecca (Kelli Garner). Mr Geary frequently calls out Justin for turning up unprepared, not having done his research, and hence not able to put any coherent arguments during the discussion. Mr Geary embarrasses Justin by calling out that he is only there to be close to Rebecca. Rebecca is suggestive to Justin and indicates that she is interested in him. Justin tries to start a relationship with her, but she rejects him after he cannot open up to her about his thumb-sucking habit. For Justin, sucking his thumb takes him to his comfortable place, free of any worries or any judgments.

At a regular checkup, Justin's orthodontist, Perry Lyman (Keanu Reeves), indicates he can tell that Justin is still sucking his thumb. Lyman says that he does not want to fix Justin's teeth again. He attempts hypnosis, coaching Justin to find his power animal (a deer) and suggesting that his thumb will taste like Echinacea. This works, and Justin finds his thumb distasteful, but falls deeper into frustration without the crutch. Justin conspires with his brother Joel (Chase Offerle) to disrupt Dr. Lyman in a bicycle race with Justin's father by shoving animal conservation posters in his face while he is riding the bike. Justin and Joel are detained by the police for his behavior and later bailed out by his parents. Justin's school counselor prods the Cobbs to give him Ritalin. While his parents wring their hands over the idea, Justin insists that he needs the help and says that if medication is the simple cure to his problems, then he should be allowed to use it.

Almost immediately after beginning treatment, Justin begins to have elevated energy, confidence and focus. He reads the Moby Dick book straight through. He begins to excel on the debate team, unseating Rebecca from the star position; she quits the team and drifts into the stoner crowd. Justin's newfound aggressiveness nets the debate team repeated awards. Simultaneously, he begins to challenge the neuroses of the adults around him, especially their struggles with aging. Justin's confidence grows to the extent that he convinces Mr Geary to let him stay in the girl's room during their debate tours, and even convinces him to buy them a 6-pack of beer. Justin heard on the news that Schramm had a cocaine addiction and has moved into a celebrity rehab facility. He is shocked to learn that Audrey has also requested a transfer to the same facility. Justin knows that Audrey has a huge crush on Schramm. Audrey says that moving to he rehab center is a huge promotion for her and it has nothing to do with Schramm. With a somewhat deceitful cover letter, Justin applies to NYU, in spite of his mother's urging that he go to college closer to home. Justin claims on his applications that his grades are below average as both his parents suffer from mental illness. Justin applies for a course in TV journalism. Justin runs into Lyman and tells him how he was diagnosed with ADHD and now he is taking medication for it.

Before the state finals, Justin's rival finds him taking Ritalin & accuses him of cheating. This shakes Justin's confidence in himself. After rambling incoherently at the state debate championship, Justin quits the debate team, throws away the pills (as he realizes that they are not a cure, but just stimulants to speed up his mental facilities), and seeks out Rebecca to hook him up with pot. Justin finds a signed photo of Schramm in one of Audrey's books in her bag and is now confirmed that Audrey is in touch with Schramm.

During their smoking sessions, Rebecca blindfolds him and engages with him in kissing and other sexual activity, which Justin interprets as a relationship. But when he broaches the subject, Rebecca tells him otherwise, calling their meetings an "experiment." She wanted to educate herself in sexual matters & chose someone like Justin who could never hurt her. He quits both her and the drugs.

Both Justin and his father suspect that Audrey is having an affair with Schramm after she is transferred to a celebrity rehab facility where Schramm has been committed. Attempting to catch his mother in the act, he instead meets Schramm sneaking a smoke in the bushes, and learns the unromantic truth that Audrey saved Schramm's life by pulling out a drug stash out of his ass that Schramm had pushed too much inside. That's why Schramm practically worships Audrey. The next day, he receives an acceptance letter from NYU.

During a final checkup, Dr. Lyman reveals to Justin his discovery that thumb-sucking is not a medically debilitating problem and says that everyone has their own flaws, and nobody has all the answers-that in fact learning to live without having the answers is (perhaps) the answer. On his flight to New York, Justin dreams of reaching his goal of being a TV anchor, "sharing the truth with the world". He wakes up after sleep talking to find his thumb in his mouth and an attractive girl smiling at him. Slightly embarrassed but self-confident, he introduces himself.