Mischa and karl 06 marie claire fm party

This week Mischa Barton was hospitalized at Cedars-Sinai Medical Center under an involuntary psychiatric hold (also known as a 5150) by the Los Angeles Police Department.

Shades of Britney Spears' famous freakout.

But Mischa's beginning was so full of promise. How did a young, beautiful and talented actress end up like this?

Let's examine the Mischa Barton mystery …Keep reading…

]]>MISCHA SUNDANCE 2001 The stunning London-born Barton was trained in New York theater and would be hailed as one of People’s 50 Most Beautiful from 2003 to 2006.

Her poor little rich girl character Marissa on “The O.C.” made her a youthful fashion icon, cover girl and trend-setter. And she became a regular at high fashion shows in New York and Paris, befriended by designers Robert Cavalli, Derek Lamb, Matthew Williamson, Karl Lagerfeld and Giorgio Armani.

She was anointed Hollywood Life’s “Breakthrough Actress of the Year” and “Entertainment Weekly’s 'It' Girl” in 2003.

Now she’s become “that girl.”

Click here to see who may have played a part in the Mischa meltdown!

And due to her being held at the Cedars psych ward this week, she missed the Thursday night New York premiere of her big comeback movie, “The Homecoming.”

To some Hollywood insiders, Mischa’s meltdown was a long time coming. She’s dated some questionable Hollywood studs — Brandon "Greasy Bear" Davis and musician Cisco Adler. She’s been linked to British rocker Luke Pritchard of the Kooks, Taylor Locke of Rooney and Brett Simon, who directed her in “Assassination of a High School President” (she appeared nude in a bathtub). Somewhere in there was rumored to be a Josh Hartnett sighting.Spl12734_002

Rumors have been circulating for over a year about Mischa’s reported increased drug and alcohol consumption, bad habits, heavy smoking, late nights hanging out with musicians and stumbling out of London and LA clubs.

Her weight — a startling gain and a sudden loss — raised eyebrows and made headlines. Then there was that embarrassing paparazzi shot of her horribly dimpled thighs while she wore a bikini. Ouch.

Back in May 2007, we got the first clue about her hard-partying ways when she was rushed to the hospital from a Malibu beach party, reportedly for a reaction to cold medicine. Later that year, she was arrested for a DUI and pot possession and received a fine and three years of unsupervised parole.

Barton later admitted she quietly sneaked away to a rehab to get a softer sentence.

She recently told Marie Claire’s British edition: “I wanted to prove to the court that I would take it completely seriously, so I went to rehab to prove I was sober. It really helped in getting the more serious aspects of my case dropped because, you know, that’s what they want to hear; you’re not an alcoholic and you don’t have a problem…. I just did the program and got through it."

Click here for a look back at Mischa's shocking fall from grace and perhaps some clues to her mysterious meltdown.

We hope Mischa gets the help she needs before anything worse happens.

More Mischa Dish:

Mischa pulls a Britney, held for psychiatric evaluation at Cedars

Mischa Barton calls police for a "medical reason"

Mischa Barton's get out of jail free card!

Get the skinny on Mischa Barton's thighs

Mischa Barton's slim down?

Photos: FilmMagic, top; WireImage, middle; LAPD mug shot.