Lindsay Lohan trying to escape

The ‘Machete’ actress – who checked into the rehabilitation facility in Los Angeles last month after failing two court-ordered drugs tests – and another person tried to flee the grounds of the clinic to buy the soft drink from a vending machine at the nearby Eisenhower Medical Center.

They were caught after the 24-year-old star’s accomplice got their clothing caught on a fence, leaving the duo needing help.

A source told website RadarOnline.com: "Lindsay and her co-conspirator were forced to give it up and flag down a volunteer, who was crossing the centre’s grounds on a golf cart.

"The pair were safely returned, decaffeinated, to their hall, where they were the centre of a process meeting over what they had done."

There is no soda dispenser at the clinic, which forbids luxuries such as caffeine and television.”

As well as Lindsay being banned from getting her caffeine drink fix, it was recently claimed staff have urged her to cut down on her use of social networking websites and email.

A source said: "Lindsay is only allowed to use her phone for two hours a day, and only to keep in touch with family and close friends.

"Before, she would repeatedly and compulsively email her friends if she was ever in a situation where she felt lonely, and she would vent on twitter."

The policy has been implemented so Lindsay can "concentrate on herself" during therapy.

Lindsay is due in court on October 22 for a probation hearing, following her failed drugs tests.

The 'Mean Girls' actress - who served 13 days of a 90-day jail term behind bars in July for breaching the terms of probation set for a 2007 driving under the influence (DUI) conviction - returned to prison following the failed tests, but ended up spending just a matter of hours behind bars after posting $300,000 bail.