A drug is a substance which has an effect bodily function, such as mental functioning, the immune system, hormonal regulation, or the circulatory system. Drugs which have a positive effect of the functioning of these systems are referred to as medicine. Drugs which have a deleterious effect are often illegal, though some drugs such as caffeine, alcohol, and tobacco are legal. Illegal drugs, despite their deleterious effect on health are often taken because of addiction or a desire to fit in.
Illegal drugs are drugs that the government has declared to be illegal. This is often based on a perception, true or otherwise, that such substances can potentially cause damage to a person's brain and other organs. Equally there is concern about the fact that most drugs cause addiction. There is much debate over the legalization of drugs, people on both ends of the political spectrum are advocating for some drugs to be legalized while others on both ends are advocating for tougher penalties for possession of drugs. Some new age hippies believe drugs can separate one's body from one's soul, and native Americans believe drugs allow one to talk to trees; current research  in neuroscience has shown that psychedelic drugs can be used to induce religious experiences .
Those in favor of legalizing drugs often argue that the negative social consequences, including gang warfare and the permeation of dangerously impure substances, are more to do with their prohibition than the drugs themselves. Indeed, before the criminalization of heroin in the UK it was no more than a trivial medical problem . Opponents of criminalization also point to the Prohibition experiment in the USA, where the illegality of alcohol caused problems of gang warfare and unsupervised distilleries that made worse the very problem that prohibition was intended to solve.
Legal recreational drugs
A small number of drugs are legally tolerated in Western democracies. Examples include alcohol, nicotine and caffeine, whereas other drugs which have less adverse affect on the body, such as ecstasy, are banned due to their social stigma.