The final years of Monroe's life were marked by illness, personal problems, and a reputation for being unreliable and difficult to work with. The circumstances of her death, from an overdose of barbiturates, have been the subject of conjecture. Though officially classified as a "probable suicide", the possibility of an accidental overdose, as well as the possibility of homicide, have not been ruled out. In 1999, Monroe was ranked as the sixth greatest female star of all time by the American Film Institute. In the years and decades following her death, Monroe has often been cited as a pop and cultural icon as well as an eminent American sex symbol.