Maggie (Anne Hathaway) is a free spirited woman, indipendent, and doesn’t want commitments. Jamie (Jake Gylenhaal) is charming, easy going and womanizer. He first worked at electronic store but he was fired when the manager caught him and his girlfriend having sex. So his brother offers him to find a job as a medical representative. Jamie is hired by Pfizer and he uses his charm to convince the doctors to prescribe Zoloft and Zithromax. He is rebuffed constantly by doctors, so he tried his best to convince Dr. Knight to prescribe Zoloft because the others will follow his lead.
Jamie meets one of Knights patient, Maggie, who suffers from Parkinson’s disease at early onset. Once again, he uses his charm with the receptionist to get the contact number of Maggie. He dated her and when they return to her apartment they have sex.
One day, in the hospital parking lot, he was confronted by one of Maggie’s lover to get away from her and the doctors. But that doesn’t stop him from seeing Maggie, that night when he is unable to get an erection, Maggie teases him that he should use Viagra. He started selling Viagra, which becomes popular with the doctors and add spice with Maggie and Jamie’s sex life.
Jamie finds himself falling in love with Maggie, but Maggie ignored his feelings at first. They argue about their relationship and she leaves. Jamie waited for her, when the bus comes back, Maggie is touched that he waited and agree to work their relationship.
Jamie asks Maggie to attend a conference. She is moved with the stories of the people who suffers the same disease. Maggie asks Jamie to join her and he meets a man with wife who’s suffering from stage 4 Parkinson’s Disease. He asks for advice but the man just tell him to find a healthy girlfriend instead. He gets confused. After the conference, Maggie tells him how much she loves him.
Jamie and Maggie finds an appointment with a specialist to have some tests done. Then one time he gets upset because their appointment was rescheduled. Maggie walks out and they fight, she insists that there is no cure. Maggie thinks that Jamie would only love her if she is healthy, so she breaks up with him.
After some time, as he is meeting Bruce, he runs into Maggie who is on a date. Bruce tells him that he is promoted to the Chicago office. As he go home and packs his things for Chicago, he finds the video he recorded with Maggie and realizes that he must go after Maggie. He looks for Maggie and he goes after her on way to Canada. He asks her to get off the bus and talks to him for 5 minutes to work things out. He tells her about she makes him a better person, that he needs her and love her. They live together again and Jamie refused the Chicago promotion, and instead continues his medical studies.