Research interviews about overdose experiences were conducted with 115 patients attending a methadone maintenance clinic in south London, UK. While almost half (49.6%) reported having experienced overdose personally (on an average of four occasions each), almost all (97.4%) reported that they had witnessed overdoses (on an average of six occasions each). This represents a total of 706 overdoses witnessed, of which 106 had resulted in fatalities. The vast majority of patients (86/97) reported that they had taken actions when they had witnessed overdoses with those acting taking an average of nearly threee different actions on the last occasion on which they had seen someone overdosing. Most respondents reported that they would be willing to act, even if they did not know the overdose victim personally and that they had not been deterred from acting by the previous response from the emergency services. Fear of punishment was not a strong deterrent from acting certainly not for this sample, with many participants also expressing an interest in expanding their repertoire of overdose interventions, for example through training in resuscitation techniques and by keeping naloxone at home for use in overdose emergency.