Bottom-up surveillance: why digital community adulteration reporting belongs in the European drug early warning architecture

Abstract Background Drug checking services have matured into a differentiated ecosystem of implementation models, from centralised laboratory surveillance to point-of-care spectroscopy, festival-based volunteer services, and postal schemes. Yet, despite their demonstrated value, these services do not reach all populations of people who use drugs equally. Evidence suggests that some groups remain under-served: socially integrated people who use stimulants, people in rural and peri-urban areas, people supplied through postal and cryptomarket channels, and people in jurisdictions where no formal service operates. In a European context increasingly marked by high-potency synthetic opioids such as nitazenes, this coverage gap has direct public health consequences. Main body This Perspective argues that digital community-based adulteration reporting platforms (crowdsourced, anonymous, near-real-time systems collecting reports of suspected adulteration and atypical effects) constitute a complementary surveillance layer that should be articulated with the Early Warning System (EWS) of the European Union Drugs Agency (EUDA) and its national equivalents. The proposal is not internationally unique, since comparable systems exist in Australia, Scotland, New Zealand and parts of the USA. The argument rests on four complementarities between chemical-analysis services and community reporting, which are epistemic, temporal, coverage-related, and infrastructural. The logic is analogous, though not identical, to the integration of syndromic and laboratory signals in infectious disease surveillance. Four implementation principles are proposed: epistemic labelling, structured metadata, strong data governance, and explicit interfaces with formal systems. Three objections are addressed. These are unreliability and noise (met through workflow and verification design), moral hazard (met from the harm reduction evidence base), and threats to anonymity from integration (met through an architecture operating only on aggregated signals under civil-society governance). Conclusions Digital community reporting does not replace chemical analysis; it operates in a complementary evidence regime that can extend reach, accelerate signal detection, and strengthen formal early warning architectures. Three policy steps are outlined: a shared reference data model (agreed vocabularies, taxonomies and export specifications enabling interoperability) under EUDA coordination, formal recognition of community reporting as preliminary evidence within the EWS, and pilot integration in member states with established drug checking architectures.