The mother of Levi Johnston, the father of former Alaska Gov. Sarah Palin's grandson, was in custody after pleading guilty to a drug charge, officials said.

In a Palmer, Alaska, courtroom Wednesday, Sherry Johnston pleaded guilty to one count of possession with intent to deliver the powerful painkiller Oxycontin, KTUU-TV, Anchorage, reported Thursday. Sentencing will be Nov. 20.

Johnston's attorney, Rex Butler, says the agreed-to sentence of three years makes her eligible to serve time at home wearing an ankle monitor and allows her doctors to treat her medical conditions, which the attorney said include scurvy because Johnston's body doesn't process vitamin C.

"She understands what's going on and she realizes she's got to pay for what occurred, and, of course again, we're just happy and thankful we got to where we are today," Butler said.