RxNorm: Clinical Drug Nomenclature & API Guide

This guide provides technical reference information on biomedical terminologies and data models; it does not constitute clinical, prescribing, or medical advice.

RxNorm is a standardized nomenclature for clinical drugs produced by the U.S. National Library of Medicine (NLM), part of the National Institutes of Health (NIH). By assigning normalized names and unique identifiers to medications, RxNorm links the names and codes used in different drug vocabularies, electronic health record (EHR) systems, and pharmacy databases.

What Is RxNorm?

In routine healthcare delivery and clinical research, the same therapeutic agent is frequently documented under numerous distinct trade names, brand variations, abbreviations, and vendor-specific database codes. For example, a clinician might prescribe “Prozac,” an EHR system might record “fluoxetine HCl,” and an outpatient pharmacy system might log a specific 11-digit National Drug Code (NDC). Because these representations obscure clinical equivalence, aggregating data across hospitals or registries can lead to fragmented medication histories.

RxNorm addresses this by providing normalized names for prescription and many over-the-counter drugs available in the United States. Distributed through the broader Unified Medical Language System (UMLS) framework, RxNorm finds drugs from the names and codes of its constituent vocabularies and maps them to shared clinical drug concepts. This supports health systems and research networks exchanging data via Fast Healthcare Interoperability Resources (FHIR).

Who Runs It and What It Covers

NLM produces RxNorm. According to the NLM overview, the full RxNorm data set is released on the first Monday of each month, and RxNorm is updated every Wednesday with newly approved drug information from the MTHSPL source vocabulary.

The scope of RxNorm, per the NLM overview:

Prescription and over-the-counter drugs: RxNorm contains the names of prescription and many over-the-counter drugs available in the United States.
Out of scope: Dietary supplements, medical devices, and homeopathics are out of scope for RxNorm.
Licensing: NLM does not charge for licensing RxNorm, although using some non-RxNorm source data may require additional licensing from those source providers.

Core Architecture: RxCUI and Term Types (TTYs)

At the center of RxNorm is the RxNorm Concept Unique Identifier (RxCUI), the identifier assigned to each RxNorm concept. NLM’s technical documentation states that retired RxCUIs are never re-used or deleted, although RxCUIs can be merged when two concepts are found to be synonyms.

RxNorm organizes medications by Term Types (TTYs). Each TTY specifies a level of granularity:

IN (Ingredient): A compound or moiety that gives the drug its distinctive clinical properties, such as Fluoxetine.
PIN (Precise Ingredient): A specified form of the ingredient that may or may not be clinically active, such as Fluoxetine Hydrochloride.
SCD (Semantic Clinical Drug): The generic product defined as Ingredient + Strength + Dose Form (for example, Fluoxetine 20 MG Oral Capsule).
SBD (Semantic Branded Drug): The branded counterpart defined as Ingredient + Strength + Dose Form + Brand Name (for example, Fluoxetine 20 MG Oral Capsule [Prozac]).
SCDC (Semantic Clinical Drug Component): Ingredient plus strength (for example, Fluoxetine 20 MG).
SCDF (Semantic Clinical Drug Form): Ingredient plus dose form, without a strength (for example, Fluoxetine Oral Capsule).
DF (Dose Form): The dose form, such as Oral Capsule or Topical Ointment.

RxNorm vs NDC: What Is the Difference?

RxNorm concepts are often compared with the National Drug Code (NDC). Both identify pharmaceuticals, but they work at different levels: an RxCUI names a clinical drug concept, while an NDC identifies a specific packaged product.

Dimension	RxNorm (RxCUI)	National Drug Code (NDC)
Level of Abstraction	Clinical drug concept (ingredient, strength, dose form)	A specific packaged product
Identifier Stability	Retired RxCUIs are never re-used or deleted	Tied to a specific labeled product
Mapping Cardinality	One RxCUI can have multiple NDCs	A single NDC is expected to be assigned to only one RxNorm clinical drug concept

Because many data sources record NDCs, studies that combine sources commonly map NDCs to RxCUIs so that the same drug concept is identified consistently. NLM’s RxNorm technical documentation describes the NDC-to-RxCUI relationships. For wider context on clinical research compliance, see clinical trial registration and reporting compliance.

Navigating with RxNav

The National Library of Medicine provides RxNav, a browser for several drug information sources, including RxNorm, RxTerms and MED-RT. It finds drugs in RxNorm from the names and codes in its constituent vocabularies. In RxNav you can:

Search by name, NDC, or RxCUI using the search box.
Browse through tabs for a graph view, RxCUI, NDC, RxTerms, and drug classes.
Filter results to human or veterinary drugs, prescribable drugs, or single-ingredient drugs.
Switch views between Classic, Simple, and Table.
Open links to DailyMed drug labels and MedlinePlus, and download results.

According to NLM, a license is not needed to view RxNorm data in RxNav.

Programmatic Access: The RxNorm API

The NLM offers the RxNorm API, a RESTful web service for retrieving RxNorm concepts, relationships and NDC information. NLM’s API page states that, with one exception, no license is needed to use it, and that use is subject to its Terms of Service. Functions listed on that page include:

findRxcuiByString (/rxcui?name=...) finds concepts that match a given name.
getAllProperties (/rxcui/{rxcui}/allProperties) returns detailed information for a concept.
getAllRelatedInfo (/rxcui/{rxcui}/allrelated) returns concepts linked to a given concept, directly or indirectly.
getNDCs (/rxcui/{rxcui}/ndcs) lists NDC codes associated with a concept.
getNDCProperties (/ndcproperties) returns details for an NDC, current and historical.
getAllHistoricalNDCs (/rxcui/{rxcui}/allhistoricalndcs) lists every NDC ever associated with a concept.

Teams that standardize drug coding in multi-site studies often document it alongside their Good Clinical Practice (GCP) processes and clinical trial protocol design.

Strengths and Limits

Strengths

No licensing fee: NLM does not charge for licensing RxNorm.
NDC crosswalks: RxNorm connects package-level NDCs to clinical drug concepts.
Explicit structure: Distinct term types separate clinical drugs (SCD) from branded drugs (SBD).

Limits

U.S. focus: RxNorm covers drugs available in the United States.
Scope exclusions: Dietary supplements, medical devices, and homeopathics are out of scope, and RxCUIs for out-of-scope drugs are transient and can change at any time.
Nomenclature only: RxNorm names and relates drugs; for labels, RxNav links to DailyMed.

Frequently Asked Questions

What is RxNorm?

RxNorm is a normalized naming system for clinical drugs produced by the U.S. National Library of Medicine. It assigns RxCUIs to drug concepts so that names and codes from different vocabularies can be linked.

What is an RxCUI?

An RxCUI (RxNorm Concept Unique Identifier) is the identifier assigned to each concept in RxNorm. Retired RxCUIs are never re-used or deleted.

What is the difference between RxNorm and NDC?

RxNorm represents the clinical drug concept (ingredient, strength, and dose form), whereas an NDC (National Drug Code) identifies a specific packaged product. One RxCUI can have multiple NDCs.

What is RxNav?

RxNav is a browser from the National Library of Medicine for several drug information sources, including RxNorm. You can search it by name, NDC, or RxCUI.

Is the RxNorm API free to use?

According to NLM, with one exception, no license is needed to use the RxNorm API, and use is subject to its Terms of Service.

Sources

National Library of Medicine. “RxNorm Overview.” Checked November 7, 2026. https://www.nlm.nih.gov/research/umls/rxnorm/overview.html
National Library of Medicine. “RxNav.” Checked November 7, 2026. https://mor.nlm.nih.gov/RxNav/
National Library of Medicine. “RxNorm APIs.” Checked November 7, 2026. https://lhncbc.nlm.nih.gov/RxNav/APIs/RxNormAPIs.html
National Library of Medicine. “RxNorm Technical Documentation.” Checked November 7, 2026. https://www.nlm.nih.gov/research/umls/rxnorm/docs/techdoc.html