2026 ICD-10-CM Diagnosis Code T43.296AUnderdosing of other antidepressants, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T43

ICD-10-CM T43.296A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T43.296A is a billable ICD-10-CM diagnosis code for underdosing of other antidepressants, 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). The code is not accepted as a principal diagnosis by the Medicare Code Editor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Underdosing of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T43.296A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of other antidepressants, initial encounter
Short Description
Underdosing of other antidepressants, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T43.296
Underdosing of other antidepressants

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances
CategoryT43Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classified
This CodeT43.296AUnderdosing of other antidepressants, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T43.296A.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Coding GuidelinesGuidance

Underdosing refers to taking less of a medication than is prescribed by a provider or a manufacturer's instruction. Codes for underdosing should never be assigned as principal or first-listed codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.

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.

CCSR INJ029
Underdosing of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Bupropion

    a propiophenone-derived antidepressant and antismoking agent that inhibits the uptake of dopamine.

  • Nomifensine

    an isoquinoline derivative that prevents dopamine reuptake into synaptosomes. the maleate was formerly used in the treatment of depression. it was withdrawn worldwide in 1986 due to the risk of acute hemolytic anemia with intravascular hemolysis resulting from its use. in some cases, renal failure also developed. (from martindale, the extra pharmacopoeia, 30th ed, p266)

  • Viloxazine

    a morpholine derivative used as an antidepressant. it is similar in action to imipramine.

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.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
AmfebutamoneT43.291T43.292T43.293T43.294T43.295T43.296
BifemelaneT43.291T43.292T43.293T43.294T43.295T43.296
BupropionT43.291T43.292T43.293T43.294T43.295T43.296
DiclofensineT43.291T43.292T43.293T43.294T43.295T43.296
MinaprineT43.291T43.292T43.293T43.294T43.295T43.296
NomifensineT43.291T43.292T43.293T43.294T43.295T43.296
OxitriptanT43.291T43.292T43.293T43.294T43.295T43.296
PrazitoneT43.291T43.292T43.293T43.294T43.295T43.296
ThiazesimT43.291T43.292T43.293T43.294T43.295T43.296
TianeptineT43.291T43.292T43.293T43.294T43.295T43.296
ViloxazineT43.291T43.292T43.293T43.294T43.295T43.296

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 T43.296A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
No Map There is no ICD-9 equivalent for this code.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T43.296AOverview

Is T43.296A (Underdosing of other antidepressants) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of other antidepressants, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T43.296A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of other antidepressants, such as an emergency visit or first evaluation.

Can T43.296A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of other antidepressants, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

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.