T40.491A Poisoning by other synthetic narcotics, accidental (unintentional), initial encounter

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

ICD-10-CM code T40.491A is identified as Poisoning by other synthetic narcotics, accidental (unintentional), initial encounter. Public sources list this code alongside related substance poisoning codes and include it within billing guidelines for naloxone injections and Medicare articles on controlled substance monitoring. The provided excerpts establish the code's official label and its appearance in administrative coding contexts. 2 4 5

Plain-language overview

The code T40.491A is labeled as Poisoning by other synthetic narcotics, accidental (unintentional), initial encounter. This code appears in a list of related opioid and narcotic poisoning codes within billing guidelines for a naloxone injection. 2

What this code represents

The official label for T40.491A is Poisoning by other synthetic narcotics, accidental (unintentional), initial encounter. A related code, T40.491D, is labeled Poisoning by other synthetic narcotics, accidental (unintentional), subsequent encounter. 2 4

Coding details

The code T40.491A is listed alongside T40.411A for fentanyl and T40.421A for tramadol. The provided excerpts list these distinct codes but do not explicitly state the clinical criteria that separate other synthetic narcotics from these named substances. 2

The code T40.491A is listed in a broader table of narcotic poisoning codes that includes Poisoning by synthetic narcotics and Poisoning by other narcotics. The excerpts present these as separate code labels without detailing their specific categorical differences. 3

Documentation considerations

The code T40.491A is included in a list of diagnosis codes within billing guidelines for Naloxone Hydrochloride Injection. The provided source text lists the code but does not explicitly state the clinical documentation needed to support its use. 2

Coverage and utilization context

The code T40.491A appears in Medicare articles titled Billing and Coding: Controlled Substance Monitoring and Drugs of Abuse Testing. The provided article text lists the code but does not explicitly state that its presence guarantees payer coverage. 4 5

What the sources add

The Centers for Disease Control and Prevention source references encounters with International Classification of Diseases codes and lists accidental poisoning codes for opioids. The provided excerpt does not explicitly state that T40.491A is used for public health surveillance. 1

The Medicaid source lists T40.491A within naloxone billing guidelines, while the Medicare sources list the code within controlled substance monitoring articles. These sources demonstrate the code appears in different administrative billing contexts. 2 4 5

Sources

1. Enhancing Identification of Opioid-involved Health ... — cdc.gov; accessed 2026-07-26.
2. Naloxone Hydrochloride Injection for Intramuscular or Subcutaneous use (Zimhi™) HCPCS code J3490: Billing Guidelines — medicaid.ncdhhs.gov; accessed 2026-07-26.
3. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-26.
4. Article - Billing and Coding: Controlled Substance Monitoring and Drugs of Abuse Testing (A57077) — cms.gov; accessed 2026-07-26.
5. Article - Billing and Coding: Controlled Substance Monitoring and Drugs of Abuse Testing (A57077) — cms.gov; accessed 2026-07-26.
6. T40.491 — Poisoning by other synthetic narcotics, accidental (unintentional) | ICD-10 Code · Eleplan — eleplan.com; accessed 2026-07-26.