Introduction
Check tags in PubMed/Medline are used to quickly identify key features of studies and study subjects, such as age groups. They are frequently incorporated in search strategies. However, such searches are reliant on check tags being dependable in their application. This study sought to evaluate some irregularities the author noticed around check tags.

Method
Searches were run in Ovid Medline for a series of commonly used check tags in records of publications from 2015 to 2024. The absolute number of records employing these tags and the proportion of records employing these tags was then compared to the results of similar searches in Embase, PsycINFO, and CINAHL.

Results
There was a sharp drop in both absolute and proportional numbers of most check tags on Medline records published over this time period. For example, use of female/ decreased from 30% of Medline records for papers published in 2019 to only 10% of records for papers published in 2023. However, PsycINFO and Embase indexing patterns differed markedly.

Discussion
The trends noted have significant implications for use of check tags for searching in PubMed or Medline. Results give insight into how indexing varies between PubMed/Medline and other commonly used biomedical databases.