This report is the outcome of a project into opioid overdoses. The remit was to focus on finding practical methods of overdose prevention. In order to fulfil this remit, a critical review of existing knowledge on overdose prevention was conducted. The report adds value to existing information by developing a methodology to classify and analyse risk and protective factors stratified by those involved (drug users, observers and organisations). The report then assesses the extent to which risk and protective factors can be potentially modified at different levels, e.g. individual, treatment setting, organisational and strategic. The report therefore has the potential to be updated as new information emerges.