Subheadings (also called “qualifiers”) are associated with main headings to describe a specific aspect of a concept. Subheadings are a way of grouping together those citations that are concerned with a particular characteristic of a subject. For example, "Liver/drug effects" indicates that the article or book is not about the liver in general, but about the effect of drugs on the liver.

The subheadings in our example citation (https://pubmed.ncbi.nlm.nih.gov/17612905/ ) are the lowercase terms to the right of the slash ( / ). These include terms such as administration & dosage, adverse effects, and drug effects.