2026 ICD-10-CM Diagnosis Code T43.205AAdverse effect of unspecified antidepressants, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T43

ICD-10-CM T43.205A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T43.205A is a billable ICD-10-CM diagnosis code for adverse effect 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) and groups to MS-DRG 917 through 918. The code is not accepted as a principal diagnosis by the Medicare Code Editor. Coders also document this condition as antidepressant drug adverse reaction. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T43.205A
Billable Status
Yes — Valid for Submission
Code Describes
Adverse effect of unspecified antidepressants, initial encounter
Short Description
Adverse effect of unspecified antidepressants, init encntr
Parent Code
T43.205
Adverse effect 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 CodeT43.205AAdverse effect of unspecified antidepressants, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T43.205A.

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.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Antidepressant drug adverse reaction
  • Selective serotonin re-uptake inhibitor withdrawal

Coding GuidelinesGuidance

When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.

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 INJ028
Adverse effects of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient Yes

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 T43.205A to ICD-9-CMHistory

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

ICD-9-CM
995.29 Adv eff med/biol NEC/NOS
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
E939.0 Adv eff antidepressants
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

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 T43.205AOverview

Is T43.205A (Adverse effect of unspecified antidepressants) a billable code?

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

What does the 7th character A in T43.205A mean?

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

What MS-DRG does T43.205A group to?

On inpatient claims, adverse effect of unspecified antidepressants, initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.

Can T43.205A be a principal diagnosis?

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

What is the ICD-9 equivalent of T43.205A?

Under the General Equivalence Mappings, adverse effect of unspecified antidepressants, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E939.0 (adv eff antidepressants). 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.