The actress, who played Blair Waldorf on the show, admits there were days she never saw the sun because the shoots often started so early and ran into the night - and she could never get used to being someone fans scrutinised over her look and fashion choices.
Now 32, Leighton tells Porter Magazine she doesn't always look back on her "Gossip Girl" years with fondness.
"I was young when I started Gossip Girl," the actress, who was 19 when she landed the role of Blair, tells the magazine. "A lot more people were suddenly around and I was being looked at.
"If you don't have the right perspective, you could definitely be confused by people being that nice to you or judging you for behaviour that's typical of a 20, 21 year old... making mistakes but having to make them very publicly.
"It's been interesting and helpful for me to look at it and examine it as an adult and go, 'I don't know if it was the healthiest environment'."
She adds, "I would get there (set) at 5am and leave at 8pm. A lot of days I didn't see the sun. Everyone has their own journey, especially in their early 20s, when they're just figuring out who they are. Because of the success of that show, I was put in a place where that journey was sped up.
"I had to figure it out quickly and with not a completely developed mind to discern between what's real and what's not, who I can trust and who I can't. I got really lucky and was able to very early find and stay friends with people who are true.
"I wouldn't trade it for anything. It's sort of a time capsule."
The show, which debuted in 2008 and ran for six seasons, recently celebrated its 10th anniversary.