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Medical Subject Headings (MeSH®) in MEDLINE®/PubMed®: A Tutorial

Pharmacological Action Terms

  • Use of a term with the Pharmacologic Action search tag [pa] instructs PubMed to OR together terms from a list made up of a PA term and the drug/substance terms known to have that action.
  • MeSH terms on the list are searched with the no explode specification, [mh:noexp], so as not to include narrower terms that might not share the pharmacological action.
  • Use this search method when you want to include retrieval for all substance terms from the pharmacological action list.


beverages [mh] AND food preservatives [pa]

  • Remember, to search for articles about one particular action of a substance, search the Pharmacological Action as a MeSH heading, to retrieve articles about the action (rather than including the list of substances). Retrieval of citations indexed before 1996 is likely to be incomplete.

Note: If you enter a MeSH term that happens to be a PA term without using a search tag, PubMed will search the term as [mh] OR [pa] OR [tw].

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