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Help: Chemicals


  1. Overview
  2. Basics
  3. Hierarchies
  4. Footnotes


CTD's chemical vocabulary is a modified subset of descriptors from the “Chemicals and Drugs” category and Supplementary Concept Records from the U.S. National Library of Medicine (NLM) Medical Subject Headings (MeSH®), a hierarchical vocabulary used to index articles for MEDLINE®/PubMed®.[1] In contrast to MeSH at NLM, CTD merged the descriptors and supplementary concepts into a single hierarchy.

The chemical vocabulary is structured as a polyhierarchic tree in which a term may appear as a node in more than one branch. A term may have different descendant terms in each branch in which it appears (although CTD combines all descendants from all branches to reflect how our data is curated, searched, and displayed).

Several branches of the original MeSH vocabulary were excluded from CTD's chemical vocabulary because they are not molecular reagents, environmental chemicals or clinical drugs (e.g., “Nucleic Acids, Nucleotides, and Nucleosides” and “Purines”). Other branches were excluded because they are simply broad chemical classes that do not contain more specific terms (e.g., “Solutions” and “Poisons”).

Top ↑ Basics

Names, Synonyms, CAS Registry Number, etc.

The name of the chemical. It may also have a CAS Type 1 Name, CAS Registry Number, and synonyms.

CAS Registry Number is a Registered Trademark of the American Chemical Society.


A short definition of this chemical (from MeSH scope notes).


A drawing of the two-dimensional structure of the chemical. Drawings are integrated from ChemIDplus®, an NLM TOXNET® resource.


The unique identifier assigned to the chemical by MeSH, linked to the MeSH record for the chemical.

Curator Notes

Comments added by a CTD curator.

Curation Status

Some chemicals do not yet have curated gene interactions and/or disease associations. Click the button to request additional curation for this chemical.

Top Interacting Genes

Specific chemical–gene and protein interactions in vertebrates and invertebrates are being curated from the published literature. This chart provides a view of the ten genes with the most curated interactions for this chemical. The colored bars are linked to corresponding interactions within the interaction report for this chemical (see the Interactions tab).

Use Term in Query

Click the Use button to add this term to the Chemical field on the query form.

Top ↑ Hierarchies

Each chemical occurs in at least one location of the hierarchy; many occur in more than one. Each ancestor path of the hierarchy is presented separately, but descendants for all paths are aggregated in a single display to reflect how data in CTD is curated, searched, and displayed.

Nodes are indented to indicate their relative level in the tree. A node marked by the + symbol has descendants in at least one of the hierarchical paths displayed on the current page. The same term may or may not have descendants, depending on each particular path in which it appears. Click a term in the ancestor path to move up the tree, or click a descendant node to move down.

If you arrived at this page from a query form, you may click the Use button to add this term to the Chemical field on the query form.

Top ↑ Footnotes

Lipscomb CE. Medical Subject Headings (MeSH). Bull Med Libr Assoc. 2000 Jul;88(3):265-6. PMID:10928714