The parents called police, and the 15-year-old girl and a 16-year-old friend were taken to Juvenile Hall in California.
The Sacramento Bee reports the girls offered to pick up milkshakes at a fast-food restaurant for the parents of one of the girls Friday.
The drug was mixed into the shakes, and the couple fell asleep. The suspicious parents picked up a drug test kit the following day.
The girls told investigators they wanted to use the Internet, which the parents shut down daily at 10 p.m.
It's unclear what the girls did online.