The actress was 16 when she first played Marissa Cooper and admits she felt like a fraud playing a "fast and loose" character while she was still a virgin.
"Being a virgin at the time in that context made me feel like a fraud," she tells Harper's Bazaar. "Here I was playing a confident character (in The O.C.) who was fast and loose and yet I was still a virgin. The kids in the show were quintessential rich, privileged American teenagers drinking, taking drugs, and of course having sex."
"I knew it was important to get this thing - my virginity - that was looming over me, the elephant in the room if you will, out of the way. I started to really worry that I couldn't play this character if I didn’t hurry up and mature a little. Did I ever feel pressured to have sex with someone? Well, after being pursued by older men in their 30s, I eventually did the deed."
Mischa reveals she started to feel sexualised as she promoted her first film, "Lawn Dogs", when she was just 11.
"My film debut, Lawn Dogs, explored themes of child molestation, and, while the crew did everything to ensure that I wasn’t exposed to the realities of what all that meant, when I did press for the film, it became clear that it was very mature content."
She then became a "strange sex symbol" in Asia two years later following the release of 1999's "Pups".
The actress reveals she hadn't even had her first period when she played a teen experiencing menstruation for the first time in the film.
"The movie blew up in Asia, and I became a strange sex symbol over there," she adds. "I was 13!"