The role of the titular Time Lord has been played by numerous actors over the years. David Tennant is the current star of the show, which began in 1963, ran until 1989, then was revived in 2005.
Davies is to write five forthcoming "Who" Christmas specials and hand over the series to producer Steven Moffat in 2010.
"I have done everything I want to do with it. I love it. It is a very adult longing too, to escape everything," Davies told The Daily Telegraph.
Davies also told the newspaper the character of the Doctor must be played by a man, regardless of how "brilliant" Amy Winehouse, Judi Dench or Lesley Sharp might
be in the part.
"I am often tempted to say 'yes' to that to placate everyone but, while I think kids will not have a problem with (a female Doctor,) I think fathers will have a problem with it because they will then imagine they will have to describe sex changes to their children," he said.