In the first half of the 20th century, some cultural and social changes, but also the passing of a criminal law which aimed at stopping the spread of drug abuse explain the changes that can be pointed in the sociology of drug users. Still comparatively elitist in the 19th century, drugs begin to spread among some parts of the working class and in social fringes. This phenomenon is due to the new part played by professional drug dealers, who lived in popular neighbourhoods and tried to win new customers. Nevertheless, the sociology of drug users remained very complex and was never only the fact of outsiders.