ICD-10 Code for Constipation: K59.00 and Other K59 Codes 

The proper constipation code is based on what the provider clearly documents. Documentation of “constipation” alone may not necessarily require the same ICD-10-CM classification as a clinical diagnosis of chronic, slow-transit, outlet dysfunction, or drug-induced illness.

The K59.0 category includes several constipation codes for FY2026, and the provider’s documentation determines which one fits the diagnosis.

This guide covers the ICD-10 code for constipation, when to use K59.00, and when the provider’s documentation supports a more specific code.

What Is the ICD-10 Code for Constipation?

The ICD 10 code for constipation is K59.0. K59.0 is a valid billable ICD-10 diagnostic code for Functional diarrhea . Choose the correct code from the more descriptive codes listed below.

For FY2026, the constipation codes are:

These codes are used in medical billing and coding and are valid for the October 1, 2025 – September 30, 2026 medical billing period. CMS also lists the identical child codes K59.0 in its ICD-10-CM documents.

Is K59.0 a Billable Code?

K59.0 is the ICD-10-CM category for constipation, but it is not specific enough to be used as a billable code. When the provider documents only “constipation” without specific diagnosis, K59.00 (Constipation, unspecified) is the appropriate billable code for FY2026.

That distinction matters because using the parent category instead of the required specific code can result in an invalid diagnosis-code submission.

K59.00 — Constipation, Unspecified

K59.00 is the primary answer when someone searches for the ICD-10 code for constipation without any documented subtype.

It is used to describe constipation when a more specific type is not noted in the medical record (i.e., slow transit, outlet dysfunction, drug-induced, or chronic idiopathic constipation). CMS materials list K59.00 Constipation, undefined The current FY2026 references tell us this is a billable code.

If no more specific constipation diagnosis is established or documented, K59.00 may be appropriate.

The key is not to infer a subtype from treatment alone. A medication, diet recommendation, or symptom pattern does not automatically establish a more specific ICD-10-CM diagnosis.

K59.01 — Slow Transit Constipation

K59.01 represents slow transit constipation. It should be used when the provider documents that specific diagnosis. Slow-transit constipation is when stool moves slowly through the colon.  Coders should not identify slow transit constipation on their own, just because a patient says infrequent bowel movements.

Why Documentation Matters

A history of infrequent bowel movements alone does not give the coder permission to convert a general constipation complaint into slow transit constipation. The code should reflect the diagnosis established and documented by the provider.

K59.02 — Outlet Dysfunction Constipation

K59.02 is the code for outlet dysfunction constipation.

This code should not be selected merely because a patient reports difficulty passing stool. The documentation should support the specific diagnosis.

K59.03 — Drug-Induced Constipation

This Code indicates constipation that has happened due to the the common side effects of drugs that are prescribed to the patient. The code instruction states to use an additional code for an adverse effect, when applicable, to identify the drug, using the appropriate T36-T50 code with the required fifth or sixth character.

What About Opioid-Induced Constipation?

This is an important distinction for anyone searching for the opioid-induced constipation ICD 10 code.

There is no unique K59 code for “opioid-induced constipation. The ICD-10-CM code is K59.03 – Drug induced constipation. If the provider documents that the constipation is induced by an opioid, K59.03 may be appropriate with the additional adverse-effect coding required by the Tabular List and Official Guidelines.

Drug-Induced Does Not Mean Poisoning

The FY2026 Official Guidelines distinguish an adverse effect from poisoning. When a correctly prescribed and properly administered drug causes an adverse effect, the code for the nature of the adverse effect is assigned first, followed by the appropriate adverse-effect code identifying the drug. Poisoning follows different sequencing rules.

Therefore, a routine medication-related constipation case should not automatically be treated as a poisoning case.

K59.04 — Chronic Idiopathic Constipation

K59.04 is chronic idiopathic constipation. The code also includes functional constipation as an inclusion term.

This is more specific than simply documenting “constipation.”

The distinction is important because a coder should not turn an unspecified diagnosis into chronic idiopathic constipation based only on how long the patient reports symptoms or on the medications prescribed. The medical record needs to support the diagnosis being coded.

K59.09 — Other Constipation

K59.09 represents other constipation. The ICD-10-CM Tabular List includes chronic constipation under this code’s applicable terminology, while K59.04 specifically identifies chronic idiopathic constipation.

This distinction deserves attention.

If the provider documents a specific constipation condition that does not correspond to K59.01, K59.02, K59.03, or K59.04, K59.09 may be appropriate.

However, K59.09 should not become a catch-all simply because the coder is uncertain. The documentation and Index/Tabular List should be reviewed before selecting an “other” code.

Constipation Coding: Specific vs. Unspecified

A practical way to approach constipation coding is to ask one question:

What exact diagnosis has the provider established?

The ICD-10-CM Official Guidelines instruct coders to report the highest level of specificity and thorough documentation that is supported by the medical record. 

How Provider Documentation Affects the Constipation Diagnosis Code

Documentation is the link between the clinical encounter and the final constipation billing code. For constipation-related encounters, useful documentation may establish:

• The provider’s actual diagnosis
• The type of constipation
• Whether the condition is chronic or idiopathic
• Whether a medication caused the constipation
• Whether a specific functional disorder has been diagnosed
• Other conditions that affected the encounter
• The reason for the evaluation or treatment

Avoid Coding From Medication Lists Alone

Suppose a patient takes an opioid and reports constipation.

The medication list may make drug-induced constipation clinically plausible, but that does not mean the coder should independently assign K59.03. The provider should document the relationship when drug-induced constipation is the diagnosis being reported.

Avoid Coding From Symptoms Alone When a Diagnosis Is Not Established

The reverse problem can also occur.

A patient may report:

• infrequent bowel movements
• hard stools
• straining
• abdominal discomfort

Those findings do not automatically establish chronic idiopathic constipation, slow transit constipation, or outlet dysfunction constipation.

If a diagnosis is not confirmed, the Official Guidelines for Outpatient Services tell coders to report the disease to the maximum degree of certainty for that contact which may include signs, symptoms, aberrant results or other cause for the visit.

When Should Constipation Not Be the Primary Diagnosis?

Constipation may be clinically significant, although not the first listed diagnosis for every encounter.

For outpatient care, the first-listed diagnosis is the diagnosis, condition, problem or other cause for the visit shown in the medical record to be largely responsible for the services delivered. Other conditions noted may be mentioned if they are present and need or affect care.

For example, a patient may have constipation during an encounter largely related to some other recognized condition. In such cases, when constipation is complicating the care, it may be stated as an extra diagnosis, but is not automatically the first-listed condition.

Likewise, fecal impaction is separately classified as K56.41, and the K59.0 category carries an Excludes1 note for fecal impaction. It should not simply be coded as unspecified constipation.

IBS with constipation is also separately classified as K58.1, rather than automatically using a K59 constipation code.

Common Constipation Coding Mistakes

Using K59.0 as the final diagnosis code.  A more specific code is required.

Defaulting to K59.00 when a specific diagnosis is documented

If the provider documents chronic idiopathic constipation, slow transit constipation, outlet dysfunction, or drug-induced constipation, the record should be evaluated for the corresponding specific code.

Assuming chronic constipation means K59.04

K59.04 is chronic idiopathic constipation, not simply every case described as chronic.

Assuming an opioid automatically means K59.03

The provider’s documentation should support the drug-induced relationship. A medication list by itself should not be used to manufacture a diagnosis.

Confusing K59.09 with K59.04

“Other constipation” and “chronic idiopathic constipation” are not interchangeable. The documented diagnosis should determine which code is appropriate.

Ignoring Excludes notes

The K59.0 category includes an Excludes1 note for fecal impaction (K56.41) and an Excludes2 note for incomplete defecation (R15.0). These instructions should be reviewed during code assignment.

Constipation Billing Considerations for Providers

Selecting an accurate diagnosis code is only one part of a clean claim. The diagnosis reported should be supported by the medical record and should correspond with the services provided.

For practices, recurring problems can arise when:

• the assessment does not match the code selected;
• documentation supports a more specific diagnosis but the claim uses an unspecified code;
• a drug-related diagnosis is reported without the required additional coding;
• the first-listed diagnosis does not reflect the reason for the outpatient service;
• related diagnoses are reported without documentation showing that they affected care.

The FY2026 Official Guidelines emphasize collaboration between providers and coders and state that accurate coding cannot be achieved without complete documentation.

Payer-specific medical-necessity and claim-processing requirements can also vary by service and payer. Those policies should be checked separately rather than treating a general ICD-10-CM rule as a universal coverage rule.

Keep Constipation Coding Aligned With the Clinical Record

The most important point in ICD 10 constipation codes is simple: code what the provider documented, not what the coder assumes.

The correct code for constipation , unspecified , documented is K59.00 . K59.01 to K59.04 are precise diagnoses of constipation and must be supported with matching documentation. K59.09 is for additional constipation not covered by the more specific alternatives. If you have a high volume of claims in your practice, having a consistent documentation and coding review process can help.

Frequently Asked Questions

What is the ICD-10 code for constipation?

The constipation category is K59.0, but the billable/specific code depends on the documented diagnosis. For unspecified constipation, the applicable code is K59.00.

Is K59.00 a billable code?

Yes. K59.00 — Constipation, unspecified is a billable/specific ICD-10-CM diagnosis code for FY2026.

Is K59.0 a billable constipation code?

No. K59.0 is the parent category for constipation. A more specific code, such as K59.00, K59.01, K59.02, K59.03, K59.04, or K59.09, should be selected when supported by the documentation.

What is the ICD-10 code for chronic idiopathic constipation?

The ICD-10-CM code is K59.04 — Chronic idiopathic constipation. Functional constipation is included under this code.

What is the ICD-10 code for opioid-induced constipation?

Opioid-induced constipation is represented under K59.03 — Drug induced constipation when the provider documents the drug-related cause. The ICD-10-CM Tabular List also instructs coders to use an additional adverse-effect code when applicable to identify the drug.

What is the ICD-10 code for other constipation?

K59.09 — Other constipation is used for other specified constipation that does not correspond to the more specific constipation codes. The documentation should support use of the “other” category rather than simply reflecting coder uncertainty.