PubChem is a free, publicly accessible chemistry database operated by the National Center for Biotechnology Information (NCBI), a division of the U.S. National Library of Medicine (NLM) within the National Institutes of Health (NIH). It is the largest open repository of small-molecule chemical structures and bioassay data in the world, and it functions as core research data infrastructure for chemistry, pharmacology, toxicology, and drug-discovery research communities. For research data managers, PubChem is a working example of a mature, domain-specific repository: it accepts depositor-submitted data, applies its own standardization and quality checks, cross-links records to related NCBI resources, and exposes everything through open programmatic interfaces.
What Is PubChem?
PubChem launched in 2004 as part of the NIH Molecular Libraries Roadmap Initiative, which funded high-throughput screening to identify small molecules (“chemical probes”) that modulate the activity of specific gene products. That origin still shapes the database’s structure: PubChem was built to hold both chemical structures and the biological assay results that describe what those structures do, linked together so a researcher can move from a compound to the experiments that tested it, and back.
PubChem is organized around three core, interlinked databases:
- PubChem Compound — unique, standardized chemical structures for small molecules, deduplicated and validated from depositor submissions, searchable by name, synonym, structure, or identifier, with computed properties (molecular weight, formula, InChI/InChIKey, canonical SMILES, and more).
- PubChem Substance — the raw records as submitted by depositors (journals, government agencies, chemical vendors, individual research groups, and screening centers), before standardization into a Compound record. A single Compound can have many corresponding Substance depositions.
- PubChem BioAssay — deposited bioactivity data and full descriptions of the assays used to generate it, including the protocol, screening conditions, and readout type, so results can be interpreted and, where relevant, reproduced or reanalyzed.
These three collections are cross-referenced with other NCBI resources — including Protein, Gene, Pathway, and Patent data — so a compound record can be traced through to the biological targets and literature associated with it.
Who Hosts and Maintains PubChem
PubChem is hosted and maintained by NCBI/NLM/NIH, the same federal agency that operates PubMed, GenBank, and the Protein Data Bank’s U.S. archiving partner, RCSB PDB. That institutional home matters for research data management purposes: PubChem is government-operated public infrastructure rather than a commercial or single-institution resource, it has no paywall or account requirement for access, and its long-term stewardship is backed by federal library and biomedical-informatics funding rather than a grant that could lapse. This is broadly the same governance model as CASRAI’s Protein Data Bank (PDB) guide describes for macromolecular structure data, and it is a useful pattern to recognize when evaluating whether a discipline-specific repository is a durable place to deposit or cite data.
Scale: How Much Data Is in PubChem
PubChem’s holdings grow continuously as new substances are deposited and new assay results are submitted, so any specific count is a snapshot rather than a stable figure. Published NIH/NCBI documentation has described PubChem’s scale in the tens of millions of unique compound structures and well over a hundred million depositor-submitted substance records, with well over a million bioassay descriptions covering tens of thousands of distinct protein targets — and those totals have continued to climb in the years since. Rather than cite a number here that will already be stale by the time this page is read, the practical guidance for researchers and data managers is: treat PubChem’s own live record counts (visible on its homepage and in its statistics documentation) as the authoritative figure, not any number reproduced secondhand, including this one.
How Researchers Use PubChem
Searching and retrieving chemical data
PubChem supports search by chemical name, synonym, structure drawing, molecular formula, and a range of standard chemical identifiers (CID for compounds, SID for substances, AID for assays, InChIKey, CAS number where available). Structure-based searching allows similarity and substructure queries, which is particularly useful for medicinal chemistry and drug-discovery workflows exploring chemical analogs.
Depositing substance and bioassay data
PubChem accepts data deposition from journals, funding agencies, screening centers, chemical vendors, and individual investigators. Depositing bioassay results to PubChem BioAssay is a common way for federally funded high-throughput screening projects and some journals’ supporting-information requirements to satisfy chemical and biological data-sharing expectations, since the deposited record becomes a permanently citable, publicly retrievable object rather than a supplementary file attached only to one publication.
Programmatic access
For larger-scale or automated use, PubChem exposes its data through the PubChem Power User Gateway (PUG), including a REST-style interface (PUG-REST) and a full SOAP/XML interface, so that data managers and software can query and retrieve records without manual web searches. This is the relevant access route for anyone integrating PubChem lookups into an electronic lab notebook, a laboratory information management system, or a data pipeline rather than doing one-off manual queries.
PubChem and the Research Data Management Lifecycle
For research data managers advising chemistry, pharmacology, or toxicology groups, PubChem is worth treating as the default, discipline-appropriate deposition target for small-molecule structures and screening/bioassay results, in the same way that PDB is the default target for macromolecular structure data, GenBank for nucleotide sequences, or a domain repository more generally is preferable to a generalist repository when a well-established, discipline-specific one exists. Depositing to PubChem rather than only publishing a compound or assay result in a paper’s supplementary materials supports several FAIR data principles in practice: the record gets a stable, resolvable identifier (its CID, SID, or AID), it is indexed and machine-searchable independent of the originating article, and it can be cross-referenced by later depositors and reusers. Funder and journal data management plans that specify a “recognized, discipline-specific repository” for chemical or bioassay data can generally point to PubChem by name.
Citing PubChem Data
PubChem records are citable objects: a Compound (CID), Substance (SID), or BioAssay (AID) record has a persistent, resolvable identifier and URL, and PubChem’s own documentation provides recommended citation formats for referencing specific records in publications, similar in principle to how any data repository record should be cited with enough specificity (identifier plus access date, at minimum) that another researcher can retrieve the exact version referenced.
Frequently Asked Questions
Is PubChem free to use?
Yes. PubChem is free and open to the public with no account, login, or subscription required to search, browse, or download data, consistent with NIH/NLM’s mission of providing free access to deposited biomedical and chemical information.
Who can deposit data to PubChem?
Depositors include government agencies, journals, chemical vendors, screening centers, and individual research groups. PubChem publishes deposition guidelines and tools (including the PubChem Upload system) for submitting substance and bioassay data.
What is the difference between a PubChem Compound and a PubChem Substance record?
A Substance record is the raw data as submitted by a depositor. A Compound record is the standardized, deduplicated chemical structure derived after PubChem processes one or more Substance depositions that describe the same underlying structure. Several Substance records from different depositors can map to a single Compound record.
Does PubChem only cover compounds relevant to drug discovery?
No. While PubChem grew out of an NIH initiative focused on chemical probes and drug discovery, its scope has expanded to include a broad range of small molecules relevant to chemistry, toxicology, environmental science, and materials research, not only pharmaceutical candidates.
How is PubChem different from PubChem BioAssay specifically?
“PubChem” is the umbrella name for the whole resource; “PubChem BioAssay” is one of its three core databases, specifically holding assay protocols and biological activity results, as distinct from PubChem Compound (structures) and PubChem Substance (raw depositor submissions).
