Mischa Barton's partying lifestyle ruined her friendship with Nicole Richie, according to a U.S. report.
The former The O.C. star was allegedly placed on involuntary psychiatric hold on Thursday, after suffering a meltdown and calling cops to her Los Angeles home the night before to attend to a "medical issue".
Reports since suggest the 23-year-old actress has alienated herself from a number of her friends and particularly grown apart from pregnant mom Richie.
An ex-pal tells U.S. magazine People, "In the last few years, her dark side has really come out. Her friends, like Nicole, want to be supportive but they really can't be around her too much. She's too volatile. It makes us sad, but we're also like, 'Pull it together and get help already."
People alleges the pair drifted apart after a party in 2007, during which Barton overindulged and was taken into hospital.
The source adds, "Most of her Hollywood friends have distanced themselves from her (since that party). After that happened, her friends thought it would be a wake-up call, but it wasn't. Nicole is focused on motherhood and her family. (She) considers (Mischa) a dear friend but she's also a mother who can't be around too much negative, unsafe behaviour. Mischa is one of the reasons that Nicole is mostly with her other mom friends these days, not the party girls."
Barton's representative has slammed rumours her "medical issue" was sparked by a three-day cocaine binge.
