Aims: This study used group psycho-education methods to assist injecting heroin users in preventing, and responding to overdose. Methods: An "OD Prevention" group was advertised in a London prescribing service and associated primary care unit. The intervention took place in a small group over one afternoon (3.5 hours), and trained participants in recognizing, and responding to heroin overdoses (defining overdose, discussing known risk factors and on-site instruction in cardio-pulmonary resuscitation (CPR). Participants were all injecting heroin users in service contact with the primary care unit, drug dependence unit, or hostels for the homeless in central London. Participants self-referred, or were referred by key workers. Participants completed pre- and post-group questionnaires concerning their personal experience of overdose, the witnessing of others' overdoses and fatalities, their current response in overdose situations, and their overall confidence in helping others who have overdosed. Findings: In total 107 people attended the group. Of these, 42% had witnessed others' overdose, and 29% had witnessed one or more deaths as a result of overdose. Following the group intervention more participants reported feeling "quite or very confident" in managing an OD situation, confident in undertaking CPR with someone who had overdosed, and were less likely to pursue "folklore" remedies to overdose. Conclusions: Using psycho-educational group approaches can be an effective tool in attempts to prevent and respond to heroin overdoses, and is seen as useful by users. (Contains 4 tables and 1 figure.)