"Methadone-Pretty" as a compound adjective describes someone who is considered attractive in a waifish manner due to the characteristic thinness of a heroine addict
(thin is "in" in many cultures, especially most of the USA).
It is difficult to give examples as most models fall into this category, but we don't think of them as being gaunt due to the way we perceive still photos (unless ribs are protruding, people never look "too thin" in photos).
One such example would be Milla Jovovich, model, singer, songwriter, actress. If the name doesn't ring a bell, one place a lot of geeks will have seen her is in the movie The Fifth Element where she had a fairly large role as Leeloo and played opposite Bruce Willis.