2026 ICD-10-CM Diagnosis Code T40.5X6AUnderdosing of cocaine, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T40

ICD-10-CM T40.5X6A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T40.5X6A is a billable ICD-10-CM diagnosis code for underdosing of cocaine, 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
T40.5X6A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of cocaine, initial encounter
Short Description
Underdosing of cocaine, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T40.5X6
Underdosing of cocaine

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
CategoryT40Poisoning by, adverse effect of and underdosing of narcotics and psychodysleptics [hallucinogens]
This CodeT40.5X6AUnderdosing of cocaine, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T40.5X6A.

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 narcotics and psychodysleptics [hallucinogens] (T40). 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

  • Cocaine

    an alkaloid ester extracted from the leaves of plants including coca. it is a local anesthetic and vasoconstrictor and is clinically used for that purpose, particularly in the eye, ear, nose, and throat. it also has powerful central nervous system effects similar to the amphetamines and is a drug of abuse. cocaine, like amphetamines, acts by multiple mechanisms on brain catecholaminergic neurons; the mechanism of its reinforcing effects is thought to involve inhibition of dopamine uptake.

  • Cocaine- and Amphetamine-Regulated Transcript Protein

    neuropeptide that functions with neuropeptide y and leptin in the regulation of appetite. it also plays a role in neural development and is involved in the regulation of energy homeostasis and stress control.

  • Cocaine Smoking

    smoking of cocaine.

  • Cocaine-Related Disorders

    disorders related or resulting from use of cocaine.

  • Crack Cocaine

    the purified, alkaloidal, extra-potent form of cocaine. it is smoked (free-based), injected intravenously, and orally ingested. use of crack results in alterations in function of the cardiovascular system, the autonomic nervous system, the central nervous system, and the gastrointestinal system. the slang term crack was derived from the crackling sound made upon igniting of this form of cocaine for smoking.

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
Coca (leaf)T40.5X1T40.5X2T40.5X3T40.5X4T40.5X5T40.5X6
CocaineT40.5X1T40.5X2T40.5X3T40.5X4T40.5X5T40.5X6
Cocaine::topical anestheticT40.5X1T40.5X2T40.5X3T40.5X4T40.5X5T40.5X6

Patient EducationClinical

Cocaine

Cocaine is a very addictive drug that is made from leaves of the coca plant found in South America. It is mostly available as an illegal drug that some people use to get high. In rare cases, it is also used as a prescription drug for for anesthesia during certain surgeries.

The full article covers:

  • What is cocaine?
  • How do people use cocaine?
  • What are the short-term effects of cocaine?
  • What are the long-term effects of cocaine?
  • Can a person overdose on cocaine?
  • What are the treatments for cocaine use disorder?

Read the full article at MedlinePlus

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

Convert T40.5X6A 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 T40.5X6AOverview

Is T40.5X6A (Underdosing of cocaine) a billable code?

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

What does the 7th character A in T40.5X6A mean?

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

Can T40.5X6A be a principal diagnosis?

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