Opioid drug related death is the topic of this thesis. Each of the published works submitted in this volume has investigated an aspect of opioid drug related death. The publications have been grouped into three sub-themes: i. Characteristics of opioid drug related deaths ii. Methadone-related deaths in and out of treatment iii. Improving the quality of treatment for opioid drug dependence: a focus on injectable opioid treatment The introduction and background (Chapter1) will briefly review-the-relevant literature on opioid drug death predating my own contribution to the field. The next chapter of the thesis, 'Publications' (Chapter 2), will comprise the body of published work being submitted for the degree of Doctor of Medicine. Each article is accompanied by text on the preceding page outlining my individual contribution to that research study. The thesis will conclude with a discussion of the published works (Discussion, Chapter 3) which summarises the chief findings and reflects on the international significance and impact of the work. Finally, the Conclusion (Chapter 4) will submit suggestions for areas of future research into opioid drug related death.