One hundred and thirty-five drug users in contact with treatment services in Scotland and England were interviewed about their experiences of witnessing overdoses - both overdoses resolved successfully and those leading to death - and actions taken to effect resuscitation. One hundred and four (77%) had witnessed a mean of 11.5 overdoses, of whom 41 (30.4% of the study sample) had witnessed an average of 4.2 fatal overdoses. A wide range of actions was reported at the most recent witnessed overdose, the most common being slapping or shaking the victim (an average of 2.5 minutes after overdose was first recognised) or walking the person around the room (3.2 minutes after recognizing overdose). There was no consistent relationship between the time taken to acting and the number of actions taken. Successful resolution of last witnessed overdose was associated more strongly with immediate onset of overdose, while those that led to death were more often those that involved slow onset of overdose. There is clear evidence of the opportunity and willingness of witnesses to intervene, particularly when overdose onset is immediate, with a wide range of strategies adopted to encourage recovery, although these may often be inappropriate and wrongly prioritized.