Heroin (or diacetylmorphine), a depressant nervous central system, is a semi-synthetic opiate. Its main adverse effect, respiratory depression, can lead to death, especially after an intravenous injection. By loss of tolerance, an overdose can be lethal following heroin use after a period of abstinence (voluntary or not). Mortality rate among heroin users is between 1 and 3%. Addiction, following a regular and continuous use, occurs in less than a quarter of persons who ever tried heroine. Heroin addicts often present with different problems (for instance, a criminal behaviour), without any obvious link with addiction. For a fraction of the addicts, addiction becomes a chronic relapsing disease, requiring a long term maintenance substitution therapy. However, relapses and sometimes continuous heroin use are frequent, For treatment resistant and severe heroin addicts, heroin-assisted treatment can be a solution. Despite the numerous available therapies, heroin is considered to be the drug with the most negative effects on the user.