T40.491 ICD-10-CM Code: Poisoning by other synthetic narcotics, accidental (unintentional)

T40.491 is the ICD-10-CM diagnosis code for poisoning by other synthetic narcotics, accidental (unintentional). T40.491 sits in the ICD-10-CM chapter for injury, poisoning and certain other consequences of external causes (s00-t88), within the section covering poisoning by, adverse effects of and underdosing of drugs, medicaments and biological substances (t36-t50).

Header codes like T40.491 cannot be reported on claims directly, they organize child codes that share clinical context but the actual diagnosis must be coded to the highest level of specificity supported by the documentation. Coders should look at T40.491's child codes and select the one that matches the patient's documented presentation, since payers reject header codes submitted as the primary diagnosis. For risk adjustment workflows, header codes never contribute to a Medicare Advantage member's RAF score on their own; only billable child codes that happen to map to a payment HCC affect risk-adjusted plan payments.