NEW YORK (AP) -- Sophia Bush is happy to be hanging with the grown-ups.
She spent nine years on the CW series "One Tree Hill," which followed a group of young people from their teens into their twenties.
Now the 31-year-old actress plays a cop closer to her own age on NBC's "Chicago P.D.," airing Wednesdays (10 p.m. EST).
"Finally!" she exclaimed in a recent interview when asked about what it means to make the transition.
"When you're working on a show whose subject matter is deemed to be teen, even though it evolved out of that, there's still an energy to it that can be very frustrating as an adult human being and it was really hard for a lot of us," she said.
"As the years went on we felt that we were growing and our characters were growing but there was still this really terrible high-school bully energy."
She said it was especially difficult for the female members of the cast.
"When (characters) Brooke and (Hilarie Burton's) Peyton were pitted against each other ... the fans on Peyton's side started hating me, not my character. And the fans that were on my side started hating Hilarie, not her character. For us as a group of friends it was really traumatic at times to see the way that people were talking about us and to not sort of be allowed to sort of get out from under that. ... We're like, `Listen, we're grown-ups who love each other! Can we please stop fighting?'"
"Chicago P.D." is a spinoff of the NBC series "Chicago Fire." It focuses on the Intelligence Unit of the Chicago Police Department. The show is produced by Dick Wolf, creator and executive producer of the "Law & Order" franchise.
"We cross over constantly," says Bush of the two shows.
"(The characters) go to the same bar to have beers after work and we very often respond to the same calls. It's really a lot of fun for us."
While Wolf's shows usually fall in the procedural category, Bush says "it's different than any cop show I've ever seen."
It's "not black and white, hero and villain," she said. "It's muddy and it's gray. ... None of our heroes are perfect."
Bush plays Detective Erin Lindsay. She says the character is the closest to her of any role she's had.
"Erin has a really strong moral compass and it's something that I understand and I relate to."