Heroin is an opioid painkiller and the 3, 6-diacetyl ester of morphine. Heroin is                                                                                            prescribed as an analgesic, cough suppressant and as an anti diarrhoeal. It is also                                                                                    used as a recreational drug for its  euphoric effects. 

                                                                                Frequent and regular administration is associated with tolerance and physical                                                                                            dependence. In some countries, it is available for prescription for long-term use as a                                                                                  form of  opioid  replacement therapy alongside counselling.

                                                                                It was originally synthesized by C. R.  Alder Wright in 1874 by adding two acetyl                                                                                        groups to the molecule of morphine, a natural product of the  opium poppy. 

                                                                                Internationally, heroin is controlled under Schedules I and IV of the Single                                                                                                  Convention on Narcotic Drugs. It is generally illegal to manufacture, possess, or sell                                                                                  heroin without a license. In 2004, Afghanistan produced roughly 87% of the world                                                                                      supply of illicit  raw opium.  However, the production rate in Mexico rose six fold                                                                                        from 2007 to 2011, making Mexico the second largest opium producer in the world.

                                                                                Administered intravenously by injection, heroin is two to four times more potent than                                                                                  morphine and is faster in its onset of action. Illicit heroin is sometimes available in a                                                                                   matte-white powder freebase form.  Because of its lower boiling point, the freebase                                                                                  form of heroin is smokable.

                                                                                 Diamorphine,  almost always still called by its original trade name of heroin in non-                                                                                    medical settings, is used as a recreational drug for the intense euphoria it induces.

                                                                                Anthropologist Michael Agar once described heroin as "the perfect whatever drug."                                                                                    Tolerance develops quickly, and increased doses are needed in order to achieve the                                                                                  same effects.

                                                                                Its popularity with recreational drug users, compared to morphine, reportedly stems from its perceived different effects. In particular, users report an intense rush,  an acute transcendent state of euphoria,  which occurs while diamorphine is being metabolized into 6-monoacetylmorphine (6-MAM) and morphine in the brain.

Some believe that heroin produces more euphoria than other opioids; one possible explanation is the presence of 6 monoacetyl-

morphine, a metabolite unique to heroin – although a more likely explanation is the rapidity of its onset. While other opioids of recreational use produce only morphine, heroin also leaves  6-MAM,  a psychoactive metabolite. However, this perception is not supported by the results of clinical studies comparing the physiological and subjective effects of injected heroin and morphine in individuals formerly addicted to opioids; these subjects showed no preference for one drug over the other. Equipotent injected doses had comparable action courses, with no difference in subjects' self-rated feelings of euphoria, ambition, nervousness, relaxation,            drowsiness, or sleepiness.

Short-term addiction studies by the same researchers demonstrated that tolerance developed at a similar rate to both heroin and                                                                                          morphine. When compared to the opioids hydromorphone, fentanyl,  oxycodone ,                                                                                      and pethidine (meperidine), former addicts showed a strong preference for heroin                                                                                      and morphine, suggesting that heroin and morphine are particularly susceptible to                                                                                    abuse and addiction. Morphine and heroin were also much more likely to produce                                                                                      euphoria and other positive subjective effects when compared to these other                                                                                              opioids. 

                                                                                Some researchers have attempted to explain heroin use and the culture that                                                                                              surrounds it through the use of sociological theories. In Righteous Dopefiend,                                                                                            Philippe Bourgois and Jeff Schonberg use anomie theory to explain why people                                                                                        begin using heroin. By analyzing a community in San Francisco, they demonstrated                                                                                  that heroin use was caused in part by internal and external factors such as violent                                                                                      homes and parental neglect. This lack of emotional, social, and financial support                                                                                        causes strain and influences individuals to engage in deviant acts, including heroin                                                                                    usage. They further found that heroin users practiced "retreatism", a behaviour first                                                                                    described by  Howard Abadinsky,  in which those suffering from such strain reject                                                                                      society's goals and institutionalized means of achieving them.