2026 ICD-10-CM Diagnosis Code T40.3X1APoisoning by methadone, accidental (unintentional), initial encounter
T40.3X1A is a billable ICD-10-CM diagnosis code for poisoning by methadone, accidental (unintentional), 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. Coders also document this condition as accidental methadone overdose. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, accidental/unintentional; External cause codes: poisoning by drug; and Opioid-related disorders.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Accidental methadone overdose
- Accidental poisoning by methadone
- Methadone overdose
- Poisoning by methadone
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 narcotics and psychodysleptics [hallucinogens] (T40). 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
Methadone
a synthetic opioid that is used as the hydrochloride. it is an opioid analgesic that is primarily a mu-opioid agonist. it has actions and uses similar to those of morphine. (from martindale, the extra pharmacopoeia, 30th ed, p1082-3)
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.
| Substance | Accidental | Self-harm | Assault | Undetermined | Adverse Effect | Underdosing |
|---|---|---|---|---|---|---|
| Amidone | T40.3X1 | T40.3X2 | T40.3X3 | T40.3X4 | T40.3X5 | T40.3X6 |
| Dolophine | T40.3X1 | T40.3X2 | T40.3X3 | T40.3X4 | T40.3X5 | T40.3X6 |
| Levo-iso-methadone | T40.3X1 | T40.3X2 | T40.3X3 | T40.3X4 | T40.3X5 | T40.3X6 |
| Methadone | T40.3X1 | T40.3X2 | T40.3X3 | T40.3X4 | T40.3X5 | T40.3X6 |
| Physeptone | T40.3X1 | T40.3X2 | T40.3X3 | T40.3X4 | T40.3X5 | T40.3X6 |
Patient EducationClinical
Medication Errors
Medicines treat infectious diseases, prevent problems from chronic diseases, and ease pain. But medicines can also cause harmful reactions if not used correctly. Errors can happen in the hospital, at the health care provider's office, at the pharmacy, or at home. You can help prevent errors by:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T40.3X1A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T40.3X1AOverview
Is T40.3X1A (Poisoning by methadone, accidental (unintentional)) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by methadone, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T40.3X1A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by methadone, accidental (unintentional), such as an emergency visit or first evaluation.
What MS-DRG does T40.3X1A group to?
When poisoning by methadone, accidental (unintentional), 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 T40.3X1A?
Under the General Equivalence Mappings, poisoning by methadone, accidental (unintentional), initial encounter converts to ICD-9-CM 965.02 (poisoning-methadone) and E850.1 (acc poison-methadone). 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.
