Over the last decade there has been an increasing awareness of comorbidity in the adult population. It is also increasingly recognised that substance misuse is increasing in young people and the older population is increasing. Prevalence estimates and clinical experience point to more younger and older addicts attending clinical services. Substance problems are associated with psychological and physical comorbidities and social difficulties across the lifespan. This leads to poorer outcome. Inadequate assessment of substance problems, prescription and over the counter medication, including interactions and compliance, in younger and older age groups leads to ineffective management. The key principles which inform the implementation of effective pharmacological and psychological treatment interventions for nicotine, alcohol and illicit drugs treatment options in adults is well established. Outcome studies in the adult population suggest patient benefit. Although limited, studies of substance misuse treatment interventions that have been carried out in younger and older age groups demonstrate improvement. Although outcome studies that have been undertaken in comorbid groups do not yet point to a particular type of intervention or service model, administration of effective interventions for substance misuse may lead to improvements, which has policy ramifications. Most of the scientific research has been carried out is in the United States which has a very different health care system and there is need for a focus on neurobiological and social research in particularly vulnerable populations.