2027 ICD-10-CM Diagnosis Code T50.991APoisoning by other drugs, medicaments and biological substances, accidental (unintentional), initial encounter
T50.991A is a billable ICD-10-CM diagnosis code for poisoning by other drugs, medicaments and biological substances, accidental (unintentional), 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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 917 through 918. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, accidental/unintentional; External cause codes: poisoning by drug; and Poisoning by drugs, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- 4-aminopyridine poisoning
- Accidental acitretin overdose
- Accidental etretinate overdose
- Accidental immunostimulant overdose
- Accidental isotretinoin overdose
- Accidental parathyroid hormone and/or parathyroid hormone derivative poisoning
- Accidental phosphodiesterase inhibitor overdose
- Accidental phosphodiesterase inhibitor poisoning
- Accidental radiopharmaceutical overdose
- Accidental radiopharmaceutical poisoning
- Acitretin overdose
- Aldehyde dehydrogenase inhibitor overdose
- Calcium regulating agent overdose
- Etretinate overdose
- Immunostimulant overdose
- Ionophore poisoning
- Isotretinoin overdose
- Phenanthrene derivative poisoning
- Phosphodiesterase inhibitor overdose
- Phosphodiesterase inhibitor poisoning
- Poisoning by aldehyde dehydrogenase inhibitor
- Poisoning caused by parathyroid hormone and/or parathyroid hormone derivative
- Radiopharmaceutical overdose
- Radiopharmaceutical poisoning
- Retinoid overdose
Coding GuidelinesGuidance
When coding a poisoning or reaction to the improper use of a medication (e.g., overdose, wrong substance given or taken in error, wrong route of administration), first assign the appropriate code from categories T36-T50. The poisoning codes have an associated intent as their 5th or 6th character (accidental, intentional self-harm, assault and undetermined). If the intent of the poisoning is unknown or unspecified, code the intent as accidental intent. The undetermined intent is only for use if the documentation in the record specifies that the intent cannot be determined. Use additional code(s) for all manifestations of poisonings.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of diuretics and other and unspecified drugs, medicaments and biological substances (T50). 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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T50.991A: its own notes plus those printed at T50, block T36-T50, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- 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: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T50
- Ainitial encounter this code
- Dsubsequent encounter
- Ssequela
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T50.991A, its category, or a range that includes it.
Excludes1 1
These codes carry an Excludes1 note naming T50.991A: they are not reported together with it, unless the two conditions are unrelated.
Use Additional Code 1
These codes say to use an additional code from the note, and T50.991A is one of the codes named.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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 T50.991A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T50.991AOverview
Is T50.991A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by other drugs, medicaments and biological substances, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character A in T50.991A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by other drugs, medicaments and biological substances, accidental (unintentional), such as an emergency visit or first evaluation.
What MS-DRG does T50.991A group to?
When poisoning by other drugs, medicaments and biological substances, accidental (unintentional), initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 918, 917, with relative weights from 0.8716 to 1.5698 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T50.991A be reported with a code from O29.3?
Not as a rule. The Excludes1 note at block T36-T50, which applies to T50.991A, lists "toxic reaction to local anesthesia in pregnancy (O29.3-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What is the ICD-9 equivalent of T50.991A?
Under the General Equivalence Mappings, poisoning by other drugs, medicaments and biological substances, accidental (unintentional), initial encounter converts to ICD-9-CM 979.9 (pois-vaccine/biolog NEC) and E858.8 (acc poisoning-drug NEC). The mapping is approximate, so confirm the match fits the documentation.
