The naloxone investigation (N-ALIVE) randomized trial commenced in the UK in May 2012, with the preliminary phase involving 5,600 prisoners on release. The trial is investigating whether heroin overdose deaths post-prison release can be prevented by prior provision of a take-home emergency supply of naloxone. Heroin contributes disproportionately to drug deaths through opiate-induced respiratory depression. Take-home emergency naloxone is a novel preventive measure for which there have been encouraging preliminary reports from community schemes. Overdoses are usually witnessed, and drug users themselves and also family members are a vast intervention workforce who are willing to intervene, but whose responses are currently often inefficient or wrong. Approximately 10% of provided emergency naloxone is thought to be used in subsequent emergency resuscitation but, as yet, there have been no definitive studies. The period following release from prison is a time of extraordinarily high mortality, with heroin overdose deaths increased more than sevenfold in the first fortnight after release. Of prisoners with a previous history of heroin injecting who are released from prison, 1 in 200 will die of a heroin overdose within the first 4 weeks. There are major scientific and logistical challenges to assessing the impact of take-home naloxone. Even in recently released prisoners, heroin overdose death is a relatively rare event: hence, large numbers of prisoners need to enter the trial to assess whether take-home naloxone significantly reduces the overdose death rate. The commencement of pilot phase of the N-ALIVE trial is a significant step forward, with prisoners being randomly assigned either to treatment-as-usual or to treatment-as-usual plus a supply of take-home emergency naloxone. The subsequent full N-ALIVE trial (contingent on a successful pilot) will involve 56,000 prisoners on release, and will give a definitive conclusion on lives saved in real-world application. Advocates call for implementation, while naysayers raise concerns. The issue does not need more public debate; it needs good science.