T42.4X Poisoning by, adverse effect of and underdosing of benzodiazepines

ICD-10-CM Code T42.4X: Poisoning by, adverse effect of and underdosing of benzodiazepines

ICD-10-CM code T42.4X represents poisoning by, adverse effects of, and underdosing of benzodiazepines. It is categorized under Chapter 19 for injuries, poisoning, and other consequences, specifically within antiepileptic, sedative, and antiparkinsonism drugs. Benzodiazepines can cause adverse effects like respiratory depression at higher doses. CMS references this code in billing articles. 4 2 3

Plain-language overview

Code T42.4X is the ICD-10-CM designation for poisoning by, adverse effect of, and underdosing of benzodiazepines. It is structured within Chapter 19 for injury, poisoning, and certain other consequences of external causes, specifically under the T36-T50 range for drugs and biological substances. 4

What this code represents

The T42.4X code falls under category T42 for poisoning by, adverse effect of, and underdosing of antiepileptic, sedative-hypnotic, and antiparkinsonism drugs. It is further classified into subcategory T42.4, which pertains specifically to benzodiazepines. 4

Clinical context

Benzodiazepines such as lorazepam, midazolam, diazepam, and clonazepam are first-line treatments for status epilepticus. When administered in higher doses, these drugs can cause adverse effects, including respiratory depression and cognitive impairment. 2

Coding details

The April 2026 reference data indicates that T42.4X has more specific child codes. The reference record lists no inclusion terms, no "code first" instruction, and no "use additional code" instruction for T42.4X. 4

Documentation considerations

A CMS billing and coding article includes the code T42.4X5D, which designates an adverse effect of benzodiazepines during an initial encounter. The article also references accidental unintentional poisoning by benzodiazepines during an initial encounter. 3

What the sources add

The CMS article references T42.4X5D within a billing and coding context for controlled substance monitoring and drugs of abuse testing, whereas the Vero source provides the structural ICD-10-CM hierarchy and code instructions without detailing specific payer billing applications. 3 4

The Vero source establishes the exact code label and hierarchical placement of T42.4X within the ICD-10-CM system, while the CMS source demonstrates the appearance of a related specific code within a Medicare billing and coding article. 4 3

Sources

1. Clinical Pharmacokinetics and Pharmacodynamics of Naloxone — pmc.ncbi.nlm.nih.gov; accessed 2026-07-25.
2. Benzodiazepines in the Management of Seizures and Status Epilepticus: A Review of Routes of Delivery, Pharmacokinetics, Efficacy, and Tolerability — pmc.ncbi.nlm.nih.gov; accessed 2026-07-25.
3. Article - Billing and Coding: Controlled Substance Monitoring and Drugs of Abuse Testing (A56645) — cms.gov; accessed 2026-07-25.
4. ICD-10-CM Code T42.4X | Vero — veroscribe.com; accessed 2026-07-25.