The Concept of Substance Use Disorders. A Commentary on ‘Defining Substance Use Disorders: Do We Really Need More than Heavy Use’ by Rehm et al.

Substance use disorders reflect more than just substance use. At one level they are patterns of behaviour, at another level they are clusters of experiences and physiological features. Substance use disorders are strongly correlated with the level of substance use, but the importance of defining them as disorders is because this determines the need for treatment (including detoxification, agonist maintenance treatment and other pharmacotherapies). The severity of a substance disorder also strongly influences the individual's prognosis. Quantification of substance use is valuable for both clinical and epidemiological purposes, but it should be as precise as possible and notions such as “heavy use over time” are not fit for purpose.