# How to Use the ICD-10 Table of Drugs and Chemicals Step by Step

URL: https://icdcodefinder.com/blog/icd-10-table-of-drugs-and-chemicals-guide  
Published: 2026-11-02  
Updated: 2026-11-02  
Author: Priya Raman, CPC, CCS-P — Code Set & Tools Editor (ICD Code Finder editorial pen name)  
Category: Coding Tools & Tips  
ICD-10-CM codes: E11.65, J96.01, K92.2, T36, T38.3X6A, T39.1X, T39.1X1A, T40.411A, T45.515A, T50, T51, T51.0X1A, T65, Y63, Z91, Z91.12, Z91.120, Z91.13  

> A step-by-step walkthrough of the ICD-10-CM Table of Drugs and Chemicals: choosing poisoning, adverse effect or underdosing, verifying codes in the Tabular List, and adding 7th characters and manifestation codes.

## Key takeaways

- The Table of Drugs and Chemicals is part of the ICD-10-CM Alphabetic Index and has four poisoning intent columns plus adverse effect and underdosing columns.
- Classify the event before opening the table: correct drug taken as prescribed is an adverse effect, improper use is a poisoning, and taking less than prescribed is underdosing.
- When poisoning intent is not documented, code it as accidental; use undetermined only when the record states intent cannot be determined.
- Always verify the table code in the Tabular List to apply placeholder X characters, the 7th character (A, D or S) and instructional notes.
- Sequencing differs: adverse effect manifestation first, poisoning T code first, and underdosing never as the principal or first-listed diagnosis.
- Unclear intent, unclear prescribing status or unexplained symptoms after a drug change are common triggers for a compliant CDI query.

The ICD-10 Table of Drugs and Chemicals is a section of the ICD-10-CM Alphabetic Index that lists substances alphabetically, each with six code columns: four poisoning intents (accidental, intentional self-harm, assault and undetermined), adverse effect and underdosing. To use it, first decide whether the event is a poisoning, an adverse effect or an underdosing, then pick the matching column. Finally, verify the code in the Tabular List and add the correct 7th character and any manifestation codes.

This guide walks through each step for the FY2027 code set, effective October 1, 2026. It is educational content, not billing-compliance or clinical advice. Always follow the ICD-10-CM Official Guidelines for Coding and Reporting, your payer policies and the provider's documentation.

## What is the ICD-10 Table of Drugs and Chemicals and where does it sit in the Index?

The Alphabetic Index has several parts. Alongside the Index to Diseases and Injuries, it contains the Table of Neoplasms, the Table of Drugs and Chemicals and the External Cause of Injuries Index. You can browse the full [ICD-10-CM Alphabetic Index](/index) online.

The drug table lists substances by generic name, many brand names and pharmacologic classes. Drugs, medicaments and biological substances point to codes in categories T36-T50. Substances chiefly nonmedicinal as to source, such as ethanol, solvents, gases and venoms, point to toxic effect codes in T51-T65.

### What do the drug table columns mean in ICD-10-CM?

Each column corresponds to a specific character in the T code. For T36-T50 codes, the 6th character (or 5th, when the code is shorter) tells you the intent or type of event.

| Column | Character in T36-T50 codes | When to use |
|---|---|---|
| Poisoning, Accidental (unintentional) | 1 | Improper use with no intent to harm, or intent not documented |
| Poisoning, Intentional self-harm | 2 | Provider documents a deliberate overdose or self-harm |
| Poisoning, Assault | 3 | Substance given by another person with intent to harm |
| Poisoning, Undetermined | 4 | Record states intent cannot be determined |
| Adverse effect | 5 | Correct drug, properly prescribed and administered |
| Underdosing | 6 | Patient took less than prescribed or instructed |

A dash in a cell means no code exists for that combination. For example, nonmedicinal substances such as gasoline have no adverse effect or underdosing codes.

## How do you choose between poisoning, adverse effect and underdosing?

This is the decision that drives every later step. Make it from the documentation before you open the table. Section I.C.19.e of the Official Guidelines defines each category.

- **Adverse effect:** the drug was correctly prescribed and properly administered, and the patient had a reaction.
- **Poisoning:** the drug was used improperly. Examples include an overdose, the wrong drug given or taken in error, the wrong route, an error in prescription or administration, a nonprescribed drug taken with a correctly prescribed drug, and an interaction of drugs with alcohol.
- **Underdosing:** the patient took less of a medication than prescribed by the provider or instructed by the manufacturer, including stopping it.

| Scenario | Category | First-listed code |
|---|---|---|
| GI bleeding on warfarin taken as prescribed | Adverse effect | The manifestation |
| Child swallows a parent's acetaminophen | Poisoning, accidental | The T code |
| Deliberate overdose documented by the provider | Poisoning, intentional self-harm | The T code |
| Benzodiazepine taken with alcohol | Poisoning | The T codes |
| Patient cut insulin doses due to cost | Underdosing | The condition, never the T code |

### What is the step-by-step workflow?

1. Read the entire record and list every substance involved.
2. Classify the event as poisoning, adverse effect or underdosing.
3. Find the substance in the table by generic name. If it is not listed, look up its drug class.
4. Choose the column that matches the classification and documented intent.
5. Verify the code in the Tabular List and read all instructional notes.
6. Add placeholder X characters as needed and the 7th character.
7. Sequence the codes and add manifestation, abuse or noncompliance codes.

## What do the intent columns mean, and what if intent is undocumented?

The four poisoning columns capture intent. Pick intent only from what the provider documents. Do not infer self-harm from the quantity taken or from a psychiatric history alone.

When intent is unknown or unspecified, the guidelines direct you to code it as accidental. The undetermined column is only for cases where the documentation specifies that intent cannot be determined. This is a common audit finding, so read the record carefully.

### Do you need a separate external cause code for intent?

No. Codes in T36-T65 are combination codes that include both the substance and the intent, per Section I.C.19.e. No additional external cause code is required to report intent for poisonings, toxic effects, adverse effects or underdosing.

You may still report external cause codes for place of occurrence, activity or status when your facility policy or payer requires them. Those codes add context, not intent.

## Why must you verify drug table codes in the Tabular List?

Section I.B.1 of the guidelines states that both the Alphabetic Index and Tabular List must be used to locate and assign a code. The ICD-10 Table of Drugs and Chemicals is part of the Index, so coding directly from it is an error.

The table usually shows a code without its 7th character. Only the Tabular List confirms the full code structure, the placeholder X and the notes that apply. For a refresher on this two-step process, see [how to use the Alphabetic Index and Tabular List](/blog/how-to-use-the-alphabetic-index-icd-10-cm).

### What does verification catch?

- **Placeholder X:** acetaminophen leads to T39.1X- because the code has fewer than six characters before the 7th. Section I.A.5 requires the X placeholder. The complete code for an accidental initial encounter is [T39.1X1A](/icd10/T39.1X1A).
- **Instructional notes:** the T36-T50 block carries notes such as code first the nature of the adverse effect and use additional codes for manifestations or underdosing details.
- **Excludes1 and Excludes2 notes:** these can redirect you, for example away from conditions classified elsewhere. Review [how to read exclusion notes](/blog/excludes1-vs-excludes2-icd-10-cm-exclusion-notes) if they trip you up.
- **New entries:** substances and codes change. Check the [FY2027 new, revised and deleted codes](/updates) for updates that affect drug codes.

You can open any category in the [Tabular List by chapter](/chapters). Chapter 19 holds T36-T65. Each code page on ICD Code Finder shows the full title, billable status, exclusion notes and 7th-character rules.

## How do 7th characters A, D and S apply to T36-T65 codes?

Every T36-T65 code requires a 7th character. Section I.C.19.a explains how to apply them.

| 7th character | Meaning | Typical use |
|---|---|---|
| A | Initial encounter | Patient is receiving active treatment for the condition |
| D | Subsequent encounter | Active treatment is complete; routine care during healing or recovery |
| S | Sequela | A complication or condition that arises as a direct result of the poisoning or adverse effect |

The 7th character reflects the treatment phase, not whether this is the patient's first visit. A patient seen by a new provider while still in active treatment still gets A.

For sequela, code the residual condition first. Then report the T code with 7th character S to show what caused it.

## Which additional codes are needed for manifestations and noncompliance?

Sequencing is different for each category. Getting it wrong changes the principal diagnosis and can affect reimbursement.

### How do you sequence an adverse effect?

Code the nature of the adverse effect first. Then add the T36-T50 code with the adverse effect character 5.

Example: a patient on warfarin, taken as prescribed, develops gastrointestinal bleeding. Report [K92.2](/icd10/K92.2) (Gastrointestinal hemorrhage, unspecified) first, followed by [T45.515A](/icd10/T45.515A) (Adverse effect of anticoagulants, initial encounter). Code the most specific manifestation the documentation supports.

### How do you sequence a poisoning?

The poisoning T code comes first, followed by codes for the manifestations. If there is also a documented diagnosis of abuse or dependence on the substance, add it as an additional code.

Example: an accidental fentanyl overdose causes acute hypoxic respiratory failure. Report [T40.411A](/icd10/T40.411A) (Poisoning by fentanyl or fentanyl analogs, accidental (unintentional), initial encounter), then [J96.01](/icd10/J96.01) (Acute respiratory failure with hypoxia).

When more than one substance is involved, code each one individually unless the table lists a combination code. For a drug taken with alcohol, report the drug poisoning and the alcohol toxic effect, such as [T51.0X1A](/icd10/T51.0X1A) (Toxic effect of ethanol, accidental (unintentional), initial encounter), when supported.

### How do you sequence underdosing?

Underdosing codes are never assigned as the principal or first-listed diagnosis. If the reduced dose causes a relapse or exacerbation, code the medical condition first.

Add noncompliance codes from subcategories Z91.12- (intentional underdosing) or Z91.13- (unintentional underdosing) to show intent, if known. If the underdosing occurred during medical care, use the complication-of-care codes in category Y63 instead.

Example: a patient with type 2 diabetes skipped insulin doses because of cost and presents with hyperglycemia. Report [E11.65](/icd10/E11.65) (Type 2 diabetes mellitus with hyperglycemia), then [T38.3X6A](/icd10/T38.3X6A) (Underdosing of insulin and oral hypoglycemic [antidiabetic] drugs, initial encounter), and [Z91.120](/icd10/Z91.120) (Patient's intentional underdosing of medication regimen due to financial hardship).

## What documentation should prompt a CDI query in drug-related cases?

The drug table only works when the record answers three questions: what substance, how it was taken and why. When any answer is missing or conflicting, a compliant query may be appropriate.

Common query triggers include:

- **Unclear intent:** nursing notes suggest a deliberate overdose, but the provider does not document intent.
- **Prescribing status unclear:** it is not stated whether the drug was taken as prescribed, which decides adverse effect versus poisoning.
- **Undocumented link:** symptoms such as bleeding, falls or altered mental status appear after a drug change without a stated cause.
- **Unnamed substance:** the record says "pills" or "overdose" without naming the drug or class.
- **Underdosing reason missing:** a skipped medication is noted, but not why, so the Z91 subcategory cannot be selected.
- **Abuse or dependence:** substance use is mentioned but not diagnosed.

Queries must be non-leading and offer clinically supported options, including "other" and "unable to determine." Use these [compliant physician query templates](/blog/compliant-physician-query-examples-cdi-templates) as a starting point. The [AI CDI query builder](/ai/query-builder) can draft a query for your review, using your own AI key.

## How can tools speed up drug table coding?

Saving common poisoning and adverse effect codes in a reusable list cuts lookup time. The [Code Set Builder](/code-sets) lets you save and share these lists. Our guide on [building an ICD-10 code set](/blog/how-to-build-an-icd-10-code-set) covers keeping them current each FY.

When you need the exact guideline wording on intent or sequencing, the [guidelines chat](/ai/guidelines-chat) can help you find it. The [Note → Codes tool](/ai/note-to-codes) can suggest candidate codes from a note. All AI suggestions need review by a qualified coder, and none replace the official code books.

For the official source files, see the [CDC NCHS ICD-10-CM page](https://www.cdc.gov/nchs/icd/icd-10-cm/) and the [CMS ICD-10 page](https://www.cms.gov/medicare/coding-billing/icd-10-codes), which host the FY2027 code set and guidelines.

## Next steps

The ICD-10 Table of Drugs and Chemicals rewards a consistent routine: classify, choose the column, verify in the Tabular List, add the 7th character and sequence correctly. Practice it on your next drug-related record.

Ready to check a code? [Look up codes free](/search), browse more [Coding Tools & Tips articles](/blog/category/coding-tools-and-tips), or compare [Free, Pro and Team plans](/pricing) for unlimited code sets and FY-update alerts.

## Frequently asked questions

**Is an allergic reaction to a correctly administered drug coded as a poisoning?**

No. If the drug was correctly prescribed and properly administered, a reaction such as a rash or anaphylaxis is an adverse effect. Code the reaction first, followed by the T36-T50 code from the adverse effect column.

**What is the difference between a toxic effect and a poisoning in ICD-10-CM?**

Poisoning codes in T36-T50 cover drugs, medicaments and biological substances. Toxic effect codes in T51-T65 cover substances chiefly nonmedicinal as to source, such as alcohol, solvents, gases and venoms. Toxic effect codes use intent characters but have no adverse effect or underdosing options.

**How do I code a poisoning that involves two or more drugs?**

Code each drug individually unless the Table of Drugs and Chemicals lists a combination code. If the same T code would describe more than one substance, assign it only once. Sequence the poisoning codes before the manifestations.

**What should I do if a specific drug is not listed in the table?**

Look for the drug's pharmacologic class in the table, which often has its own entry. Confirm the class with the provider documentation or a pharmacy reference, then verify the code in the Tabular List. If the drug or class is unclear, consider asking the provider or pharmacy for clarification.

**Does documentation of drug toxicity always mean poisoning?**

Not necessarily. The word toxicity alone does not decide the column. If the drug was taken as prescribed and the patient developed toxicity, review guidelines and documentation carefully, as this may be an adverse effect; if there was an overdose or error, it is a poisoning. Query the provider when the record does not make this clear.

**Which 7th character applies when a poisoning patient moves to a rehab facility?**

If the patient has completed active treatment and is receiving routine care during healing or recovery, 7th character D for subsequent encounter generally applies. Use S only when coding a late effect that remains after the acute phase. Follow Section I.C.19.a and your facility's policy.

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Disclaimer: ICD Code Finder is an informational tool and is not a substitute for professional coding judgment, payer policy, or the official ICD-10-CM classification and guidelines. Not affiliated with, endorsed by, or sponsored by CMS, NCHS, or the World Health Organization. AI suggestions require review by a qualified coder.