Substance use disorder

Substance use disorder (SUD) is the clinical category for a pattern of use that continues despite meaningful impairment or harm, defined by eleven criteria covering loss of control, escalating priority given to use, and physiological adaptation. It replaced the older distinction between substance abuse and substance dependence when the DSM-5 was published in 2013, collapsing two separate diagnoses into one dimensional framework.

Severity is determined by how many criteria are met rather than which substance is involved: two or three qualify as mild, four or five as moderate, and six or more as severe. Substance-specific variants — opioid use disorder, alcohol use disorder, stimulant use disorder — apply the same framework to a particular class without changing its structure.

Physiological dependence alone does not establish the diagnosis. Tolerance and withdrawal are two of the eleven criteria, but both are excluded from the count when a substance is taken as prescribed. A person who develops tolerance to a medication in the course of treatment does not thereby meet criteria.

How it is done

Assessment is carried out through a structured clinical interview in which a clinician reviews each of the eleven criteria against the person's experience over the preceding twelve months. Brief validated screening tools — such as the AUDIT for alcohol or the DAST for other substances — can identify cases that warrant a full interview, but screening alone does not produce a diagnosis.

No laboratory test confirms or rules out the disorder. The criteria are behavioural and experiential: they describe what a pattern of use does to a person's life, relationships, and functioning. Information from multiple sources — self-report, physical examination for signs of active use or withdrawal, collateral accounts — improves the reliability of the overall picture.

What it cannot tell you

The diagnosis describes a current pattern at one point in time. It does not predict trajectory — severity can shift in either direction, and the same person may meet criteria at one point and not another. A mild-severity diagnosis is not a lesser version of a severe one; it reflects a different number of criteria met, not a different kind of disorder.

The framework does not explain why the pattern developed. Two people can carry the same diagnosis with different substance histories, comorbidities, social contexts, and physiological vulnerabilities. SUD describes the shape of the problem; it does not identify its cause.

There is also a boundary effect. The diagnosis requires at least two criteria. Harmful use that falls below that threshold — one clear consequence with no others — is not captured by the category, but is not without risk. The label does not cover the full range of use that causes harm.

Finally, the carve-out for prescribed substances is narrower than it appears. Tolerance and withdrawal are excluded from the count when a substance is taken as prescribed, but the remaining nine criteria still apply. A person can meet criteria related to craving, role impairment, or time spent on a prescribed medication even when the physiological criteria are set aside.