Cigarettes

Cigarettes are known to be a both a stimulant and a relaxant. They can improve concentration and trigger the release of key neurotransmitters in the brain, among them Dopamine, which is responsible for feelings of pleasure. These traits made cigarettes a popular habit up through the mid-20th century.

Then it was, of course, revealed that cigarettes cause a whole raft of nasty side effects, including lung cancer and yellowed teeth. Studies also showed cigarettes to be highly addictive, and very difficult to quit. For these reasons, cigarette smoking has become far less frequent in modern society, especially within the United States.