Adding Treatment-Continuity Metrics to Opioid Toxicity Investigation: A Triangulation Hypothesis for Applied Toxicology.

Fatal opioid toxicity is proximally mediated by respiratory depression, but whether an opioid exposure becomes lethal depends on opioid identity, dose, potency, route, tolerance, co-intoxicants, naloxone availability, and the response environment. Interruption of opioid agonist treatment (OAT) may alter several of these conditions through medication-uncovered time, withdrawal-driven re-exposure, tolerance change, and loss of clinical contact. We position treatment continuity as an additional time-varying exposure for overdose investigation, not as a substitute for or presumed priority over recent release from custody, treatment cessation, polydrug use, use in isolation, or lack of naloxone. We hypothesize that adding a time-resolved OAT continuity timeline to established person-, agent-, and environment-level variables will improve identification of modifiable pathways to fatal and nonfatal opioid toxicity. Its contribution is expected to vary by OAT medication and dose, treatment phase, supervised or take-home delivery, accessibility, and accompanying interventions. We propose triangulation across postmortem or clinical toxicology, longitudinal treatment and dispensing records, health and correctional data, and structured event review. A Haddon matrix organizes determinants across pre-event, event, and postevent phases. Core measures include documented OAT coverage-gap days, time to reassessment and relinkage, dose and delivery conditions, transition context, co-intoxicants, naloxone coverage, and rescue timing. Taiwan is presented as an instructive access setting rather than a universal delivery model. The hypothesis is testable through linked time-updated cohorts, within-person analyses, policy evaluations, and structured mortality and near-fatal-event review.