Drug discontinuation is an exposure transition that can prevent continuing treatment-related harm while generating, revealing, or coinciding with new adverse outcomes. Interpretation is difficult because withdrawal syndromes, rebound effects, recurrence of the treated disorder, delayed treatment-related injury, and unrelated illness can share clinical features and overlapping observation windows. This original, nonempirical analysis extends causal reasoning about medication cessation by specifying when familiar adverse-reaction and dechallenge assumptions become insufficient. Evidence from discontinuation trials, comparative cohorts, biological investigations, guidelines, and pharmacovigilance methodology is used selectively to distinguish mechanisms and their observable signatures. The proposed classification connects five rival explanations to exposure trajectories, pretreatment and on-treatment baselines, mechanism-relevant measurements, longitudinal comparators, and competing causes. It permits concurrent explanations and an unresolved category when evidence is insufficient. Its contribution is a set of conditional attribution rules and discriminating tests, not a validated diagnostic instrument. Post-discontinuation reporting should preserve the difference between temporal occurrence, mechanistic plausibility, and causal attribution; prospective testing is required before the approach is used to assign event-level probabilities.
IJPRAS
