Purpose The recent influx of interest in and the changing status of drug checking has led us to reconsider some fundamental questions about drug checking. This commentary aims to define drug checking. It proceeds in three parts: terminology, definitions and programmes that are excluded from the definition of drug checking that still have value for harm reduction.

Design/methodology/approach To inform the commentary, an informal review of pertinent publications on the topic was conducted to extract relevant definitions and terminology.

Findings Drug checking services (DCS) have five necessary features: (1) aim of reducing harm; (2) analyse samples directly from the public; (3) return results to the service user; (4) involve information exchange between service user and DCS; and (5) conduct a tailored intervention with the service user. Variable features include the populations served, setting, analysis methods, immediacy of results, nature of intervention, levels of engagement with other stakeholder groups, funding models, legal status and staff skillsets. Programmes that are not DCS but have some similarities to DCS include non-publicly accessible testing of drugs as well as testing of bodily fluids where results may inform drug alerts.

Originality/value Drug checking remains a legally, politically and commercially sensitive health service. Reflecting on the history and evolution of drug checking, both as a term and as a harm reduction service, helps provide clarity in terms of what drug checking is and what it is not. This facilitates more effective framing of evaluations, in terms of what DCS aim to do and achieve.