Product substitution is usually evaluated through pharmacological equivalence, economic consequences, policy acceptance, and adherence. These perspectives incompletely represent what substitution may change for a person who has learned to recognize and use a medicine through recurring visual, textual, tactile, contextual, and routine cues. A pharmaceutically equivalent replacement can preserve therapeutic intent while altering the recognition work required before the next dose is taken. This conceptual article develops a Human-Factors Recognition-Disruption Model to explain that transition. The model distinguishes cue change from recognition mismatch, mismatch from error, and error vulnerability from actual harm. It proposes that substitution becomes safety-relevant when altered product cues conflict with an existing recognition schema and require cognitive reconciliation through memory, written information, pharmacy communication, medication records, or other verification resources. Successful reconciliation can restore confident and correct use; unresolved uncertainty can instead produce hesitation, additional checking, inappropriate rejection, or conditions in which omission, duplication, or misselection becomes more plausible. The model therefore rejects both visual determinism and the assumption that pharmacological equivalence makes presentation changes behaviorally irrelevant. Its central implication is that safe substitution depends partly on how product change is made recognizable, interpretable, and verifiable within the patient's medication-use system. Research should consequently measure recognition disruption and reconciliation directly rather than infer them from adherence or switching outcomes alone.
