I'm not exactly sure what you mean by the dictators, but a very good example of a 20th Century dictator (who, in my opinion, should count as one of the dictators of the 20th Century, but doesn't because no-one seems to care about Africa) who took drugs would be Macias Nguema of Equatorial Guinea, who drank bhang and all sorts of hallucinogens, to such a degree that he effectively went completely insane and killed a very large proportion of his own population over a period of around a decade.

His wikipedia page gives a pretty good and comprehensive guide of what kind of man he was, but this is also worth a read.