According to RadarOnline.com, the Hollywood wild-child was caught trying to flee the Betty Ford Centre, in Rancho Mirage, California, with another patient.
The 24-year-old ex-jailbird apparently wanted to sneak into the grounds of nearby Eisenhower Medical Centre where she could grab a can of her usual tipple - Coca Cola - from a machine.
And it seems the Mean Girls actress, who is currently trying to kick her drugs habit during a month long stint of in-house treatment, almost got away with it.
She was only rumbled when her accomplice got some clothing caught on a fence.
'Lindsay and her co-conspirator were forced to give it up and they flagged down a volunteer who was crossing the centre's grounds on a golf cart,' a source told the website.
'The pair was safely returned, decaffeinated, to their hall, were they were the centre of a process meeting over what they had done.'
There is no drinks machine at the Betty Ford clinic because luxuries such as caffeine, along with phone calls and television, are strictly prohibited.
The troubled starlet is now on her fifth rehab stint after being jailed for three cocaine related incidents.