Asymmetric evidence in harm reduction: behavioural adaptation and net-effect evaluation

This preprint develops a conceptual argument about evidence standards in harm-reduction evaluation. Harm-reduction interventions can produce important proximal benefits, including reduced acute harms, prevention of death, infection prevention and improved service contact. The paper argues that evidence of proximal benefit is often allowed to carry a broader claim: that interventions do not alter drug use, behavioural adaptation or the wider risk environment in which drug use occurs. Drawing on risk-environment thinking, dual-system accounts of addiction and rational-choice models, the essay argues that the key evaluative question is not whether harm reduction is good or bad in the abstract, but what its net effects are, for whom, over what horizon and through which mechanisms. Companion preprint: Advocacy capture of inference in policy-relevant health science: when moral commitments govern empirical claims. DOI: https://doi.org/10.5281/zenodo.20102506