Severe intoxication or overdose with opiate drugs is a medical emergency.'Overload' of central nervous system (CNS) mu (µ) receptors may lead to respiratory depression and death. Many such deaths occur in longerterm injecting opiate misusers who have recently lost their tolerance through a period of abstinence, and fail to account for this when re-starting use of opiates, often following release from prison. However, opiate overdose and death may occur with any route of delivery and also involves individuals who have not lost their tolerance; for example an exceptionally pure batch of heroin may become available which is not recognised as such by the user.