Drugs and creativity

Continuous use of Drugs by creative heads like Kurt Cobain,Charlie Parker,Janis Joplin etc fostered popular impression that drug use enhances creativity.Though still it has not been scientifically proved,it is believed that :

Alcoholenhances creativity by reducing inhibitions.
Nicotineconsumption leads to certain cognitive gains in areas such as information processing speed and working memory function
Marijuanaapparently results in increased originality but has a negligible or slightly negative impact on creative achievement.