Introduction. In recent years, regional drug markets have shifted toward synthetic and polysubstance use patterns, while the toxic burden on healthcare systems has increased. As a result, registration-based indicators are increasingly diverging from the actual scale of harm. Purpose. To substantiate and validate the Monitoring Divergence Index (IDM) as a quantitative measure of misalignment between registration and toxicological monitoring contours, and to assess its prognostic association with mortality from fatal poisonings. Materials and methods. We performed a retrospective analysis of regional data from the Kabardino-Balkarian Republic for 2014–2024 IDM was calculated as the ratio of the number of cases of acute poisoning with narcotic drugs and psychoactive substances registered in year t, taken into account in the toxicological contour of regional monitoring (Tₜ), to the number of newly identified cases of addiction syndrome (F11–F19) in the same year (Pₜ). Thresholds were determined by the interquartile range using Tukey’s rule. Associations were assessed with Spearman’s rank correlation and 95% confidence intervals, with lag analysis at 1 and 2 years, and interrupted time series (ITS) analysis. For the final 2024 verification, Pₜ was aligned with the official annual count from Form No. 11. Results. The study revealed a restructuring of the regional drug scene, a 294% increase in polysubstance use, a decline in the proportion of newly diagnosed cases (rₛ ≈ –0.88; p