2026 ICD-10-CM Diagnosis Code T43.206AUnderdosing of unspecified antidepressants, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T43

ICD-10-CM T43.206A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T43.206A is a billable ICD-10-CM diagnosis code for underdosing of unspecified 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
T43.206A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of unspecified antidepressants, initial encounter
Short Description
Underdosing of unspecified antidepressants, init encntr
Parent Code
T43.206
Underdosing of unspecified 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 CodeT43.206AUnderdosing of unspecified antidepressants, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T43.206A.

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

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
AntidepressantT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::monoamine oxidase inhibitorT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::selective serotonin norepinephrine reuptake inhibitorT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::selective serotonin reuptake inhibitorT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::specified NECT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::tetracyclicT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::triazolopyridineT43.201T43.202T43.203T43.204T43.205T43.206
Antidepressant::tricyclicT43.201T43.202T43.203T43.204T43.205T43.206

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 T43.206A 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 T43.206AOverview

Is T43.206A (Underdosing of unspecified antidepressants) a billable code?

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

What does the 7th character A in T43.206A mean?

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

Can T43.206A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of unspecified 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.