Writer and director Seung-wook Byeon, who had previously served as assistant director on Peppermint Candy (1999), spent five years working on the screenplay for Sa-rang-hal-ddae-e-ya-gi-ha-neun-geot-ddeul (2006). His intention for the film was to focus on real-life issues and avoid the predictability of other melodramas, saying, "We tried to cut down on sentimental stuff as much as possible and tried to fill that space with an emotional one".
In the "surprise kiss" scene, Han Suk-kyu was required to spin Kim Ji-Soo around in a commanding way, but this took much trial and error for the duo to get the desired movement. The scene was later singled out by The Chosun Ilbo as one of the "outstanding" film kisses of the season.
The film's original working title was Miyeol (meaning "Slight Fever"), a reference to the lead character's occupation as a pharmacist. However, a series of online surveys prompted a change, with people finding the title either too vague or confusing, or not representative of the film's romantic themes.