Heroin overdose is a major cause of death among heroin users, and often occurs in the company of other users. However, sudden death after injection is rare, giving ample opportunity for intervention. Naloxone hydrochloride, an injectable opioid antagonist which reverses the respiratory depression, sedation and hypotension associated with opioids, has long been used to treat opioid overdose. Experts have suggested that, as part of a comprehensive overdose prevention strategy, naloxone should be provided to heroin users for peer administration after an overdose. A trial could be conducted to determine whether this intervention improves the management of overdose or results in a net increase in harm (by undermining existing prevention strategies, precipitating naloxone-related complications, or resulting in riskier heroin use).