Douglas, 33, the oldest child of film star Michael Douglas, has battled an addiction to drugs for years. He pleaded guilty in January 2010 to heroin possession and conspiracy to distribute drugs out of a Manhattan hotel.
He was originally sentenced to five years in prison, but with the additional time added to his sentence Wednesday isn't expected to be released until 2019 at the earliest.
E! News said Douglas' lawyer and his father's publicist were unavailable for comment.