2026 ICD-10-CM Diagnosis Code T42.4X6AUnderdosing of benzodiazepines, initial encounter
T42.4X6A is a billable ICD-10-CM diagnosis code for underdosing of benzodiazepines, 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 T42.4X6A.
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
Alprazolam
a triazolobenzodiazepine compound with antianxiety and sedative-hypnotic actions, that is efficacious in the treatment of panic disorders, with or without agoraphobia, and in generalized anxiety disorders. (from ama drug evaluations annual, 1994, p238)Bromazepam
one of the benzodiazepines that is used in the treatment of anxiety disorders.Chlordiazepoxide
an anxiolytic benzodiazepine derivative with anticonvulsant, sedative, and amnesic properties. it has also been used in the symptomatic treatment of alcohol withdrawal.Clobazam
a benzodiazepine derivative that is a long-acting gaba-a receptor agonist. it is used as an antiepileptic in the treatment of seizures, including seizures associated with lennox-gastaut syndrome. it is also used as an anxiolytic, for the short-term treatment of acute anxiety.Clonazepam
an anticonvulsant used for several types of seizures, including myotonic or atonic seizures, photosensitive epilepsy, and absence seizures, although tolerance may develop. it is seldom effective in generalized tonic-clonic or partial seizures. the mechanism of action appears to involve the enhancement of gamma-aminobutyric acid receptor responses.Clozapine
a tricylic dibenzodiazepine, classified as an atypical antipsychotic agent. it binds several types of central nervous system receptors, and displays a unique pharmacological profile. clozapine is a serotonin antagonist, with strong binding to 5-ht 2a/2c receptor subtype. it also displays strong affinity to several dopaminergic receptors, but shows only weak antagonism at the dopamine d2 receptor, a receptor commonly thought to modulate neuroleptic activity. agranulocytosis is a major adverse effect associated with administration of this agent.Diazepam
a benzodiazepine with anticonvulsant, anxiolytic, sedative, muscle relaxant, and amnesic properties and a long duration of action. its actions are mediated by enhancement of gamma-aminobutyric acid activity.Diazepam Binding Inhibitor
an 86-amino acid polypeptide, found in central and peripheral tissues, that displaces diazepam from the benzodiazepine recognition site on the gamma-aminobutyric acid receptor (receptors, gaba). it also binds medium- and long-chain acyl-coa esters and serves as an acyl-coa transporter. this peptide regulates lipid metabolism.Receptors, GABA-A
cell surface proteins which bind gamma-aminobutyric acid and contain an integral membrane chloride channel. each receptor is assembled as a pentamer from a pool of at least 19 different possible subunits. the receptors belong to a superfamily that share a common cysteine loop.Estazolam
a benzodiazepine with anticonvulsant, hypnotic, and muscle relaxant properties. it has been shown in some cases to be more potent than diazepam or nitrazepam.Flunitrazepam
a benzodiazepine with pharmacologic actions similar to those of diazepam that can cause anterograde amnesia. some reports indicate that it is used as a date rape drug and suggest that it may precipitate violent behavior. the united states government has banned the importation of this drug.Flurazepam
a benzodiazepine derivative used mainly as a hypnotic.Lorazepam
a benzodiazepine used as an anti-anxiety agent with few side effects. it also has hypnotic, anticonvulsant, and considerable sedative properties and has been proposed as a preanesthetic agent.Medazepam
a benzodiazepine derivative used in the treatment of anxiety. it has sedative, muscle relaxant, and anticonvulsant properties. one of its metabolites is diazepam and one of its excretion products is oxazepam.Midazolam
a short-acting hypnotic-sedative drug with anxiolytic and amnestic properties. it is used in dentistry, cardiac surgery, endoscopic procedures, as preanesthetic medication, and as an adjunct to local anesthesia. the short duration and cardiorespiratory stability makes it useful in poor-risk, elderly, and cardiac patients. it is water-soluble at ph less than 4 and lipid-soluble at physiological ph.Nitrazepam
a benzodiazepine derivative used as an anticonvulsant and hypnotic.Nordazepam
an intermediate in the metabolism of diazepam to oxazepam. it may have actions similar to those of diazepam.Oxazepam
a benzodiazepine used in the treatment of anxiety, alcohol withdrawal, and insomnia.Prazepam
a benzodiazepine that is used in the treatment of anxiety disorders.Temazepam
a benzodiazepine that acts as a gamma-aminobutyric acid modulator and anti-anxiety agent.Triazolam
a short-acting benzodiazepine used in the treatment of insomnia. some countries temporarily withdrew triazolam from the market because of concerns about adverse reactions, mostly psychological, associated with higher dose ranges. its use at lower doses with appropriate care and labeling has been reaffirmed by the fda and most other countries.
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 T42.4X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T42.4X6AOverview
Is T42.4X6A (Underdosing of benzodiazepines) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of benzodiazepines, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T42.4X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of benzodiazepines, such as an emergency visit or first evaluation.
Can T42.4X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of benzodiazepines, 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.
