2026 ICD-10-CM Diagnosis Code T43.616AUnderdosing of caffeine, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T43

ICD-10-CM T43.616A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T43.616A is a billable ICD-10-CM diagnosis code for underdosing of caffeine, 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
T43.616A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of caffeine, initial encounter
Short Description
Underdosing of caffeine, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T43.616
Underdosing of caffeine

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 CodeT43.616AUnderdosing of caffeine, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T43.616A.

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

  • Caffeine

    a methylxanthine naturally occurring in some beverages and also used as a pharmacological agent. caffeine's most notable pharmacological effect is as a central nervous system stimulant, increasing alertness and producing agitation. it also relaxes smooth muscle, stimulates cardiac muscle, stimulates diuresis, and appears to be useful in the treatment of some types of headache. several cellular actions of caffeine have been observed, but it is not entirely clear how each contributes to its pharmacological profile. among the most important are inhibition of cyclic nucleotide phosphodiesterases, antagonism of adenosine receptors, and modulation of intracellular calcium handling.

  • Cytochrome P-450 CYP1A2

    a cytochrome p450 enzyme subtype that has specificity for relatively planar heteroaromatic small molecules, such as caffeine and acetaminophen.

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
CaffeineT43.611T43.612T43.613T43.614T43.615T43.616

Patient EducationClinical

Caffeine

Caffeine is a bitter substance that occurs naturally in more than 60 plants including:

The full article covers:

  • What is caffeine?
  • What are caffeine's effects on the body?
  • What are the side effects from too much caffeine?
  • What are energy drinks, and why can they be a problem?
  • Who should avoid or limit caffeine?
  • What is caffeine withdrawal?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert T43.616A 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 T43.616AOverview

Is T43.616A (Underdosing of caffeine) a billable code?

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

What does the 7th character A in T43.616A mean?

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

Can T43.616A be a principal diagnosis?

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