2026 ICD-10-CM Diagnosis Code T40.2X6AUnderdosing of other opioids, initial encounter
T40.2X6A is a billable ICD-10-CM diagnosis code for underdosing of other opioids, 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
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T40.2X6A.
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.
Clinical InformationClinical
Codeine
an opioid analgesic related to morphine but with less potent analgesic properties and mild sedative effects. it also acts centrally to suppress cough.Dextrorphan
dextro form of levorphanol. it acts as a noncompetitive nmda receptor antagonist, among other effects, and has been proposed as a neuroprotective agent. it is also a metabolite of dextromethorphan.Ethylmorphine
a narcotic analgesic and antitussive. it is metabolized in the liver by ethylmorphine-n-demethylase and used as an indicator of liver function.Ethylmorphine-N-Demethylase
a drug-metabolizing enzyme of the hepatic microsomal oxidase system which catalyzes the oxidation of the n-methyl group of ethylmorphine with the formation of formaldehyde.Etorphine
a narcotic analgesic morphinan used as a sedative in veterinary practice.Hydrocodone
narcotic analgesic related to codeine, but more potent and more addicting by weight. it is used also as cough suppressant.Hydromorphone
an opioid analgesic made from morphine and used mainly as an analgesic. it has a shorter duration of action than morphine.Glucuronosyltransferase
a family of enzymes accepting a wide range of substrates, including phenols, alcohols, amines, and fatty acids. they function as drug-metabolizing enzymes that catalyze the conjugation of udpglucuronic acid to a variety of endogenous and exogenous compounds. ec 2.4.1.17.Morphine
the principal alkaloid in opium and the prototype opiate analgesic and narcotic. morphine has widespread effects in the central nervous system and on smooth muscle.Morphine Dependence
strong dependence, both physiological and emotional, upon morphine.Morphine Derivatives
analogs or derivatives of morphine.Receptors, Opioid, mu
a class of opioid receptors recognized by its pharmacological profile. mu opioid receptors bind, in decreasing order of affinity, endorphins, dynorphins, met-enkephalin, and leu-enkephalin. they have also been shown to be molecular receptors for morphine.Oxycodone
a semisynthetic derivative of codeine.Oxymorphone
an opioid analgesic with actions and uses similar to those of morphine, apart from an absence of cough suppressant activity. it is used in the treatment of moderate to severe pain, including pain in obstetrics. it may also be used as an adjunct to anesthesia. (from martindale, the extra pharmacopoeia, 30th ed, p1092)Thebaine
a drug that is derived from opium, which contains from 0.3-1.5% thebaine depending on its origin. it produces strychnine-like convulsions rather than narcosis. it may be habit-forming and is a controlled substance (opiate) listed in the u.s. code of federal regulations, title 21 part 1308.12 (1985). (from merck index, 11th ed)
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.
Patient EducationClinical
Medication Errors
Medicines treat infectious diseases, prevent problems from chronic diseases, and ease pain. But medicines can also cause harmful reactions if not used correctly. Errors can happen in the hospital, at the health care provider's office, at the pharmacy, or at home. You can help prevent errors by:
Read the full article at MedlinePlus
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Convert T40.2X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T40.2X6AOverview
Is T40.2X6A (Underdosing of other opioids) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of other opioids, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T40.2X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of other opioids, such as an emergency visit or first evaluation.
Can T40.2X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of other opioids, 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.
