2026 ICD-10-CM Diagnosis Code T42.3X4APoisoning by barbiturates, undetermined, initial encounter
T42.3X4A is a billable ICD-10-CM diagnosis code for poisoning by barbiturates, undetermined, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, undetermined; External cause codes: poisoning by drug; and Poisoning by drugs, initial encounter.
Code Identity
Code Classification
Coding GuidelinesGuidance
When coding a poisoning or reaction to the improper use of a medication (e.g., overdose, wrong substance given or taken in error, wrong route of administration), first assign the appropriate code from categories T36-T50. The poisoning codes have an associated intent as their 5th or 6th character (accidental, intentional self-harm, assault and undetermined). If the intent of the poisoning is unknown or unspecified, code the intent as accidental intent. The undetermined intent is only for use if the documentation in the record specifies that the intent cannot be determined. Use additional code(s) for all manifestations of poisonings.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs (T42). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Barbital
a long-acting barbiturate that depresses most metabolic processes at high doses. it is used as a hypnotic and sedative and may induce dependence. barbital is also used in veterinary practice for central nervous system depression.Hexobarbital
a barbiturate that is effective as a hypnotic and sedative.Mephobarbital
a barbiturate that is metabolized to phenobarbital. it has been used for similar purposes, especially in epilepsy, but there is no evidence mephobarbital offers any advantage over phenobarbital.Pentobarbital
a short-acting barbiturate that is effective as a sedative and hypnotic (but not as an anti-anxiety) agent and is usually given orally. it is prescribed more frequently for sleep induction than for sedation but, like similar agents, may lose its effectiveness by the second week of continued administration. (from ama drug evaluations annual, 1994, p236)Phenobarbital
a barbituric acid derivative that acts as a nonselective central nervous system depressant. it potentiates gamma-aminobutyric acid action on gaba-a receptors, and modulates chloride currents through receptor channels. it also inhibits glutamate induced depolarizations.Secobarbital
a barbiturate that is used as a sedative. secobarbital is reported to have no anti-anxiety activity.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Poisoning
A poison is any substance that is harmful to your body. You might swallow it, inhale it, inject it, or absorb it through your skin. Any substance can be poisonous if too much is taken. Poisons can include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T42.3X4A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T42.3X4AOverview
Is T42.3X4A (Poisoning by barbiturates, undetermined) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by barbiturates, undetermined, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T42.3X4A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by barbiturates, undetermined, such as an emergency visit or first evaluation.
What MS-DRG does T42.3X4A group to?
When poisoning by barbiturates, undetermined, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of T42.3X4A?
Under the General Equivalence Mappings, poisoning by barbiturates, undetermined, initial encounter converts to ICD-9-CM 967.0 (poisoning-barbiturates) and E980.1 (undeterm pois-barbiturat). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
