LA Country Sheriff's deputies stopped Garrett when they noticed the 1970s child star "shaking and sweating profusely" as he was about to enter a subway car, Steve Whitmore, a sheriff's spokesman told The LA Times.
At first Garrett denied having any drugs and consented to a search, but later told deputies he had black tar heroin hidden in his shoe, according to the paper.
This is not Garrett's first brush with the law -- in 2006 is he was arrested on another LA subway for possession of heroin. In 1999, he was arrested after allegedly trying to buy narcotics from undercover officers, and in 1979 he was arrested for drunk driving after an accident that left a victim permanently disabled.
Garrett was charged on Friday and is due in court on February 24.