ICD-10-CM Code Z91.13

Patient's unintentional underdosing of medication regimen

Version 2020 Non-Billable Code

Not Valid for Submission

Z91.13 is a "header" nonspecific and non-billable code code, consider using a code with a higher level of specificity for a diagnosis of patient's unintentional underdosing of medication regimen. The code is NOT valid for the year 2020 for the submission of HIPAA-covered transactions.

ICD-10:Z91.13
Short Description:Patient's unintentional underdosing of medication regimen
Long Description:Patient's unintentional underdosing of medication regimen

Consider the following ICD-10 codes with a higher level of specificity:

  • Z91.130 - Patient's unintentional underdosing of medication regimen due to age-related debility
  • Z91.138 - Patient's unintentional underdosing of medication regimen for other reason

Tabular List of Diseases and Injuries

The Tabular List of Diseases and Injuries is a list of ICD-10 codes, organized "head to toe" into chapters and sections with guidance for inclusions, exclusions, descriptions and more. The following references are applicable to the code Z91.13:

Code First

Code First
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists, there is a "use additional code" note at the etiology code, and a "code first" note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
  • underdosing of medication T36 T50

Type 1 Excludes

Type 1 Excludes
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
  • adverse effect of prescribed drug taken as directed- code to adverse effect
  • poisoning (overdose) -code to poisoning

Code Classification

  • Factors influencing health status and contact with health services (Z00–Z99)
    • Persons with potential health hazards related to family and personal history and certain conditions influencing health status (Z77-Z99)
      • Personal risk factors, not elsewhere classified (Z91)

Code History

  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016
    (First year ICD-10-CM implemented into the HIPAA code set)
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020

Information for Patients


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

  • Knowing your medicines. When you get a prescription, ask the name of the medicine and check to make sure that the pharmacy gave you the right medicine. Make sure that you understand how often you should take the medicine and how long you should take it.
  • Keeping a list of medicines.
    • Write down all of the medicines that you are taking, including the names of your medicines, how much you take, and when you take them. Make sure to include any over-the-counter medicines, vitamins, supplements, and herbs that you take.
    • List the medicines that you are allergic to or that have caused you problems in the past.
    • Take this list with you every time you see a health care provider.
  • Reading medicine labels and following the directions. Don't just rely on your memory - read the medication label every time. Be especially careful when giving medicines to children.
  • Asking questions. If you don't know the answers to these questions, ask your health care provider or pharmacist:
    • Why am I taking this medicine?
    • What are the common side effects?
    • What should I do if I have side effects?
    • When should I stop this medicine?
    • Can I take this medicine with the other medicines and supplements on my list?
    • Do I need to avoid certain foods or alcohol while taking this medicine?

Food and Drug Administration


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