2026 ICD-10-CM Diagnosis Code T42.6X6AUnderdosing of other antiepileptic and sedative-hypnotic drugs, initial encounter
T42.6X6A is a billable ICD-10-CM diagnosis code for underdosing of other antiepileptic and sedative-hypnotic drugs, 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 T42.6X6A.
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 antiepileptic, sedative- hypnotic and antiparkinsonism drugs (T42). 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
Bromine
a halogen with the atomic symbol br, atomic number 35, and atomic weight 79.904. it is a volatile reddish-brown liquid that gives off suffocating vapors, is corrosive to the skin, and may cause severe gastroenteritis if ingested.Bromine Compounds
inorganic compounds that contain bromine as an integral part of the molecule.Bromine Radioisotopes
unstable isotopes of bromine that decay or disintegrate emitting radiation. br atoms with atomic weights 74-78, 80, and 82-90 are radioactive bromine isotopes.Bromisovalum
a sedative and mild hypnotic with potentially toxic effects.Chlormethiazole
a sedative and anticonvulsant often used in the treatment of alcohol withdrawal. chlormethiazole has also been proposed as a neuroprotective agent. the mechanism of its therapeutic activity is not entirely clear, but it does potentiate gamma-aminobutyric acid receptors response and it may also affect glycine receptors.Chlormezanone
a non-benzodiazepine that is used in the management of anxiety. it has been suggested for use in the treatment of muscle spasm.Ethchlorvynol
a sedative and hypnotic that has been used in the short-term management of insomnia. its use has been superseded by other drugs.Glutethimide
a hypnotic and sedative. its use has been largely superseded by other drugs.Paraldehyde
a hypnotic and sedative with anticonvulsant effects. however, because of the hazards associated with its administration, its tendency to react with plastic, and the risks associated with its deterioration, it has largely been superseded by other agents. it is still occasionally used to control status epilepticus resistant to conventional treatment. (from martindale, the extra pharmacopoeia, 30th ed, p608-9)Primidone
a barbiturate derivative that acts as a gaba modulator and anti-epileptic agent. it is partly metabolized to phenobarbital in the body and owes some of its actions to this metabolite.Dipsacales
an order of dicotyledonous flowering plants which includes six families. it is best known for its ornamental plants such as lonicera (honeysuckle), viburnum (arrowwood and guelder rose), and scabiosa (scabious, or pincushion flower).Valerian
a plant genus of the family valerianaceae, order dipsacales, subclass asteridae, class magnoliopsida. it is best known for the sedative use and valepotriate content of the roots. it is sometimes called garden heliotrope but is unrelated to true heliotrope (heliotropium).Valerianaceae
the valerian plant family of the order dipsacales, subclass asteridae, class magnoliopsida that is characterized by 3-5-lobed tubular flowers, often spurred at the base and clustered in tight heads.Valerianella
a plant genus of the family valerianaceae. it is sometimes called goosefoot cornsalad but should not be confused with true goosefoot (chenopodium).Valproic Acid
a fatty acid with anticonvulsant and anti-manic properties that is used in the treatment of epilepsy and bipolar disorder. the mechanisms of its therapeutic actions are not well understood. it may act by increasing gamma-aminobutyric acid levels in the brain or by altering the properties of voltage-gated sodium channels.Vigabatrin
an analogue of gamma-aminobutyric acid. it is an irreversible inhibitor of 4-aminobutyrate transaminase, the enzyme responsible for the catabolism of gamma-aminobutyric acid and is used as an anticonvulsant. (from martindale the extra pharmacopoeia, 31st ed)Zolpidem
an imidazopyridine derivative and short-acting gaba-a receptor agonist that is used for the treatment of insomnia.
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
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T42.6X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T42.6X6AOverview
Is T42.6X6A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of other antiepileptic and sedative-hypnotic drugs, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T42.6X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of other antiepileptic and sedative-hypnotic drugs, such as an emergency visit or first evaluation.
Can T42.6X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of other antiepileptic and sedative-hypnotic drugs, 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.
