ObjectivesSubstance use disorder treatment is a complex problem. Complex problems require complex interventions, ideally tested via randomised controlled trials.MethodsComplex interventions are best developed in stages, using established implementation frameworks.Results and ConclusionsStarting with a historical patient case study, we explore how treatment of this challenging population group has been approached, how an evidence-based framework has informed formulation of a complex health intervention and how this has been progressed via the UK’s Medical Research Council (MRC) approach.