'The O.C.' star Adam Brody got so 'bored' with the show that the writers gave Seth a marijuana addiction to 'explain his lethargy on-screen'

• Adam Brody became so bored by season three of "The O.C." that it became evident in his performance. 
• "We were like, 'Well, how do we explain his lethargy on-screen?'"  show creator Josh Schwartz said. 
• To address his lower energy and enthusiasm, Seth starts smoking weed. 

"The O.C." star Adam Brody became so disinterested in the show by season three that the writers gave his character, Seth Cohen, a weed addiction to explain the actor's lack of enthusiasm on-screen.

"Brody just changed his delivery, his investment in it," show creator Josh Schwartz said in the book "Welcome to the O.C.: The Oral History," released on Tuesday and written by Alan Sepinwall, Schwartz, and executive producer Stephanie Savage. "His style shifted to such a degree that we felt like we needed to account for it creatively."

"The O.C.," which premiered on Fox in August 2003 and ended in February 2007 after four seasons, centers on a 17-year-old named Ryan Atwood (Ben McKenzie) who moves from a rough part of Chino, California to live with the Cohen family in their mansion in Newport Beach.

In becoming part of the Cohen family, Ryan also forms a brotherly bond with their awkward but lovable son, Seth.

After the super-sized first season of "The O.C." filled with 27 episodes and widely regarded as the show's best, the teen drama experienced a decline.

By season three, "The O.C." became bogged down by a faster production schedule, increased network involvement and pressure that impacted the storytelling, and growing detachment from the younger cast members.

According to the oral history book, Schwartz and the actors didn't have the same energy and interest that they brought to season one.

Savage said that the on-set vibe during season three was drastically different than season one, with the cast "being very lackluster, starting to be a bit petulant with directors, having an attitude, reading a book during rehearsal instead of paying attention."

The actors also disliked the scripts that season.

The core four stars of the show — McKenzie, Brody, Mischa Barton (Marissa Cooper), and Rachel Bilson (Summer Roberts) — were also inundated by movie offers, which they had to turn down due to their commitment to the show.

"I remember going to the set of the first episode of that season, and nobody was into it," Schwartz said. "There was a real sense of exhaustion and ennui from day one, which I shared."

Brody, in particular, was visibly and vocally dissatisfied during season three.

Executive producer Bob DeLaurentis described Brody as "generally unhappy most of the time."

"I think we started to get bored," Brody said, adding that regardless, he was "polite to everyone" and punctual. "But I think I very much let my distaste for the later episodes be known. I didn't mask that at all, and I'm sure I openly mocked it a bit. So I'm not proud of that."

"I started to be creatively less interested," he said. "I blame myself for a lack of professionalism, and a disrespect to the work."

In the book, Schwartz said that Brody was so disengaged during season three that he delivered a performance with less energy, which was uncharacteristic of Seth.

So, during season three, episode 13 ("The Pot Stirrer"), this shift was addressed by Seth trying marijuana for the first time in the hopes of alleviating his anxiety about leaving Newport and starting college.

"We were like, 'Well, how do we explain his lethargy on-screen? And at least if we can write that he's stoned, then we're not trying to write around it,'" Schwartz explained.