PubMed Search

Search PubMed/MEDLINE (36M+ citations) via NCBI E-utilities REST API.

API Endpoints

Base: https://eutils.ncbi.nlm.nih.gov/entrez/eutils/

esearch -- Search and get PMIDs

curl -s "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?db=pubmed&term=COVID-19+vaccine+efficacy&retmax=10&retmode=json"

Parameters: db=pubmed, term= (URL-encoded query), retmax= (default 20, max 10000), retstart= (pagination), retmode=json, sort=relevance|pub_date, mindate=/maxdate= (YYYY/MM/DD), datetype=pdat.

efetch -- Retrieve records by PMID

curl -s "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=39142890,39088712&retmode=xml&rettype=abstract"

einfo -- Database metadata

curl -s "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/einfo.fcgi?db=pubmed&retmode=json"

Query Syntax

Boolean: AND, OR, NOT, parentheses for grouping.

Field tags: [ti] title, [tiab] title/abstract, [au] author, [mesh] MeSH heading, [majr] MeSH major topic, [pt] publication type, [dp] date, [la] language, [jour] journal.

MeSH terms: Standardized vocabulary with automatic explosion to narrower terms. Use [mesh:noexp] for exact heading only. Qualifiers: /therapy, /diagnosis, /epidemiology, /genetics, /prevention and control.

Example: "Breast Neoplasms"[mesh] AND "Drug Therapy"[mesh]

Rate Limiting

• Without API key: 3 requests/sec
• With NCBI_API_KEY: 10 requests/sec (append &api_key=${NCBI_API_KEY})
• Register at: https://www.ncbi.nlm.nih.gov/account/settings/

Two-Step Search Pattern

PMIDS=$(curl -s "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?db=pubmed&term=QUERY&retmax=5&retmode=json" \
  | python3 -c "import sys,json; d=json.load(sys.stdin); print(','.join(d['esearchresult']['idlist']))")
curl -s "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=${PMIDS}&retmode=xml&rettype=abstract"

Specialty Search Patterns

• Oncology: "Neoplasms"[mesh] AND "immunotherapy"[tiab] AND "Clinical Trial"[pt]
• Cardiology: "Cardiovascular Diseases"[mesh] AND "meta-analysis"[pt]
• Neurology: "Alzheimer Disease"[mesh] AND "biomarkers"[tiab] AND 2020:2024[dp]
• Infectious Disease: "Anti-Bacterial Agents"[mesh] AND "Drug Resistance"[mesh]
• Genetics: "Genome-Wide Association Study"[pt] AND "Diabetes Mellitus, Type 2"[mesh]
• Systematic Reviews: "systematic review"[ti] AND "Randomized Controlled Trial"[pt]

Best Practices

1. Start broad, narrow with MeSH terms and field tags.
2. Use retmax=5 for exploration, increase for comprehensive searches.
3. URL-encode queries (spaces as +, quotes as %22).
4. Check count in esearch results before paginating.
5. Document exact query strings for systematic review reproducibility.
6. For systematic reviews, use "systematic review"[ti] combined with study type filters.

Zero-Hallucination Rule

NEVER fabricate results from training data. Every paper title, author, DOI, PMID, citation count, and metadata detail presented to the user MUST come from an actual API response in this conversation. If the API returns no results or partial data, report exactly what was returned. Do not "fill in" missing details from memory.