The former 'O.C.' actress - who was placed under an involuntary psychiatric hold in Los Angeles earlier this year - is dating aspiring actor Leo Wyndham.
A source said: "They've been together for over a month now. Leo is out there trying to make it as an actor, so they move in similar circles. He's been an extremely positive influence on her."
It is understood the couple, both 23, met in New York after Mischa came out of hospital.
Despite claims her wild-partying led to her being cared for on a psychiatric ward, Mischa has insisted she was hospitalised after an operation on her wisdom teeth went wrong.
She claims she was in a huge amount of pain following the botched surgery, which left her struggling to cope with her hectic work schedule.
She said: "Really, it was blown out of proportion. It's kind of silly now to be talking about it because I'm so fine now, but it was just a really bad time for me. I had two surgeries - I had four teeth taken out and it had gone really badly wrong - they had to drill into my jaw and I was just in excruciating pain. I was having Novocaine shots every day to minimise the pain. It really was rock bottom."
"If you go into the hospital, and you're having a meltdown, and you say something like, 'I feel like I want to die,' they hold you - they won't let you go," she added.
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