John Marsden PhD is professor of addiction psychology at the Addictions Department, Institute of Psychiatry, Psychology and Neuroscience, Kings College London (KCL), UK. John is a clinical research and cognitive behavioural psychologist, holding professional appointments in the addictions field since 1987. His research interests focus on: the development and evaluation of cognitive behavioural and medication assisted therapies for opioid, stimulant and alcohol use disorders; clinical epidemiology and public health; and health systems research. At KCL, John has held research grants from the English Department of Health, the Medical Research Council, the National Institute for Health Research, and investigator imitated educational grant funding from Indivior PLC to develop personalised interventions for opioid use disorder. John is the senior academic advisor, Division of Alcohol, Drugs, Tobacco and Justice, Health Improvement, Public-Health England. He is a clinical consultant to the Clinical Trials Network, National Institute for Drug Abuse, USA; and he is visiting professor at the Department of Psychiatry, Chulalongkorn University, Bangkok, Thailand. Professor Masden is Deputy Editor-in-Chief of the scientific journal ADDICTION.