According to Alaska State Troopers, Sherry Johnston - the mother of an 18-year-old Levi Johnston, who plans to marry Alaska Gov. Sarah Palin's pregnant daughter, Bristol - has been arrested on drug charges.

In September, Palin, the GOP nominee for vice president, had announced Bristol, was pregnant and Levi Johnston was the father. Bristol is due to give birth this weekend, and she and Levi Johnston have said they plan to marry.

On Thursday, Sherry Johnston was taken into custody at her home in Wasilla, Alaska, after an undercover narcotics investigation. She was released from jail in Palmer on $5,000 bail, and was not scheduled to be immediately arraigned.

Trooper spokeswoman Megan Peters said the 42-year-old Johnston has been charged with six felony drug counts - of misconduct involving a controlled substance.

Though initially the troopers did not identify the drug, Peters said late Friday in a news release that the drug was OxyContin, a strong prescription painkiller.

Peters also said no one else had been charged. She refused to release any more information about the case, saying police needed to protect the investigation.