2026 ICD-10-CM Diagnosis Code T43.1X1APoisoning by monoamine-oxidase-inhibitor antidepressants, accidental (unintentional), initial encounter
T43.1X1A is a billable ICD-10-CM diagnosis code for poisoning by monoamine-oxidase-inhibitor antidepressants, 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. 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 Poisoning by drugs, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Accidental iproniazid overdose
- Accidental iproniazid poisoning
- Accidental isocarboxazid overdose
- Accidental isocarboxazid poisoning
- Accidental moclobemide overdose
- Accidental moclobemide poisoning
- Accidental phenelzine overdose
- Accidental phenelzine poisoning
- Accidental poisoning by monoamine oxidase inhibitors
- Accidental tranylcypromine overdose
- Accidental tranylcypromine poisoning
- Iproniazid overdose
- Iproniazid poisoning
- Isocarboxazid overdose
- Isocarboxazid poisoning
- Moclobemide overdose
- Moclobemide poisoning
- Overdose of monoamine oxidase inhibitor
- Phenelzine overdose
- Phenelzine poisoning
- Poisoning by monoamine oxidase inhibitor
- Tranylcypromine overdose
- Tranylcypromine poisoning
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 psychotropic drugs, not elsewhere classified (T43). 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
Iproniazid
an irreversible inhibitor of monoamine oxidase types a and b that is used as an antidepressive agent. it has also been used as an antitubercular agent, but its use is limited by its toxicity.Carboxylesterase
carboxylesterase is a serine-dependent esterase with wide substrate specificity. the enzyme is involved in the detoxification of xenobiotics and the activation of ester and of amide prodrugs.Isocarboxazid
an mao inhibitor that is effective in the treatment of major depression, dysthymic disorder, and atypical depression. it also is useful in the treatment of panic disorder and the phobic disorders. (from ama, drug evaluations annual, 1994, p311)Moclobemide
a reversible inhibitor of monoamine oxidase type a; (rima); (see monoamine oxidase inhibitors) that has antidepressive properties.Nialamide
an mao inhibitor that is used as an antidepressive agent.Phenelzine
one of the monoamine oxidase inhibitors used to treat depression; phobic disorders; and panic.Tranylcypromine
a propylamine formed from the cyclization of the side chain of amphetamine. this monoamine oxidase inhibitor is effective in the treatment of major depression, dysthymic disorder, and atypical depression. it also is useful in panic and phobic disorders. (from ama drug evaluations annual, 1994, p311)
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
Antidepressants
Antidepressants are prescription medicines to treat depression. Depression is more than feeling a little sad or "blue" for a few days. It's a very common, serious medical illness that affects your mood and general mental health It can make you feel tired, hopeless, worried, or fearful. It can change your thinking, sleeping, and eating.
The full article covers:
- What are antidepressants?
- Are antidepressants used for other conditions?
- What are the different types of antidepressants?
- Which type of antidepressant is right for me?
- How long do antidepressants take to work?
- How long will I need to take an antidepressant?
- What are the side effects of antidepressants?
- What can I do to take antidepressants safely?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T43.1X1A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T43.1X1AOverview
Is T43.1X1A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by monoamine-oxidase-inhibitor antidepressants, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T43.1X1A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by monoamine-oxidase-inhibitor antidepressants, accidental (unintentional), such as an emergency visit or first evaluation.
What MS-DRG does T43.1X1A group to?
When poisoning by monoamine-oxidase-inhibitor antidepressants, 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 T43.1X1A?
Under the General Equivalence Mappings, poisoning by monoamine-oxidase-inhibitor antidepressants, accidental (unintentional), initial encounter converts to ICD-9-CM 969.01 (pois monoamine oxidase) and E854.0 (acc poison-antidepressnt). 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.
