Smoking is one of the most common forms of taking drugs for pleasure. Tobacco smoking is by far the most popular form of smoking today and is practiced by over one billion people in the majority of human societies. Most drugs that are smoked are considered to be addictive. The percentage of smokers has declined in the developed world but continues to rise in developing countries. The percentage of smokers have dropped by half from 1965 to 2006, falling from 42% to 20.8% in adults.