1. National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience, King’s College London , Addictions Sciences Building, 4 Windsor Walk, London SE5 8BB, UK
2. School of Public Health Sciences, University of Waterloo , 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
3. School of Public Health, Rutgers, The State University of New Jersey , 683 Hoes Lane West, Piscataway, NJ 08854, USA
4. Cancer Prevention and Control, Lombardi Comprehensive Cancer Center, Georgetown University , 3800 Reservoir Road NW, Washington, DC 20007, USA