1. Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
2. Centre for Health Services Research, Faculty of Medicine, The University of Queensland, Brisbane, QLD, Australia
3. Institute of Epidemiology and Health Care, University College London, London, UK
4. Global Drug Survey, London, UK
5. South London and Maudsley NHS Foundation Trust, London, UK