T42 – Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs

ICD-10-CM 2027 diagnosis code · Poisoning by, adverse effects of and underdosing of drugs, medicaments and biological substances

Non-billable header

ICD-10-CM code T42

Code: T42 (claims format: T42)
Description: Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs
Short description: Antiepileptic, sedative- hypnotic and antiparkinsonism drugs
Billable: No – use a more specific code below
Valid for: Dates of service October 1, 2026 – September 30, 2027 (FY2027)
Chapter: 19. Injury, poisoning and certain other consequences of external causes (S00-T88)
Block: T36-T50 Poisoning by, adverse effects of and underdosing of drugs, medicaments and biological substances

Billable codes under T42

T42 is a header code and cannot be used on claims. Choose the most specific code:

T42.0 – Poisoning by, adverse effect of and underdosing of hydantoin derivativesHeader (more codes below)
T42.1 – Poisoning by, adverse effect of and underdosing of iminostilbenesHeader (more codes below)
T42.2 – Poisoning by, adverse effect of and underdosing of succinimides and oxazolidinedionesHeader (more codes below)
T42.3 – Poisoning by, adverse effect of and underdosing of barbituratesHeader (more codes below)
T42.4 – Poisoning by, adverse effect of and underdosing of benzodiazepinesHeader (more codes below)
T42.5 – Poisoning by, adverse effect of and underdosing of mixed antiepilepticsHeader (more codes below)
T42.6 – Poisoning by, adverse effect of and underdosing of other antiepileptic and sedative-hypnotic drugsHeader (more codes below)
T42.7 – Poisoning by, adverse effect of and underdosing of unspecified antiepileptic and sedative-hypnotic drugsHeader (more codes below)
T42.8 – Poisoning by, adverse effect of and underdosing of antiparkinsonism drugs and other central muscle-tone depressantsHeader (more codes below)

7th character values

Codes in this category need a 7th character to describe the encounter or episode of care (use placeholder X for empty positions).

Character	Meaning
`A`	initial encounter
`D`	subsequent encounter
`S`	sequela

Notes for T42

Excludes2 (not included here):

drug dependence and related mental and behavioral disorders due to psychoactive substance use (F10.--F19.-)

7th character note:

The appropriate 7th character is to be added to each code from category T42

Notes inherited from parent codes

Instructional notes at a category or block level apply to every code below it.

Block T36-T50

Includes:

adverse effect of correct substance properly administered
poisoning by overdose of substance
poisoning by wrong substance given or taken in error
underdosing by (inadvertently) (deliberately) taking less substance than prescribed or instructed

Excludes1 (not coded here):

toxic reaction to local anesthesia in pregnancy (O29.3-)

Excludes2 (not included here):

abuse and dependence of psychoactive substances (F10-F19)
abuse of non-dependence-producing substances (F55.-)
immunodeficiency due to drugs (D84.821)
drug reaction and poisoning affecting newborn (P00-P96)
pathological drug intoxication (inebriation) (F10-F19)

Code first:

, for adverse effects, the nature of the adverse effect, such as:
adverse effect NOS (T88.7)
aspirin gastritis (K29.-)
blood disorders (D56-D76)
contact dermatitis (L23-L25)
dermatitis due to substances taken internally (L27.-)
nephropathy (N14.0-N14.2)

Use additional code:

code(s) to specify:
manifestations of poisoning
underdosing or failure in dosage during medical and surgical care (Y63.6, Y63.8-Y63.9)
underdosing of medication regimen (Z91.12-, Z91.13-)

Notes:

The drug giving rise to the adverse effect should be identified by use of codes from categories T36-T50 with fifth or sixth character 5.

Frequently asked questions

What is ICD-10 code T42?

T42 is the ICD-10-CM code for poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs, in the block T36-T50 (Poisoning by, adverse effects of and underdosing of drugs, medicaments and biological substances).

Is T42 a billable code?

No. T42 is a header code with more specific child codes; report one of the billable codes listed above.

Source: CDC/NCHS ICD-10-CM FY2027 code files, tabular list and index. Reference only – code assignment must follow the official ICD-10-CM guidelines and documentation in the medical record.