LC Subject Headings makes research much more efficient and effective..
LCSH is a standardized, controlled vocabulary used in most library catalogs. These terms are used in the Subject metadata field in all of the resource records. The use of these normalized subjects makes it possible for the researcher (you) to find resources on the same topic even though authors, scholars and even you might use any number of other words for the same concept. See also MeSH Headings.
Search the Library of Congress Subject Headings to obtain more accurate as well as additional terminology to assist in finding more resources. LCSH will identify variant terms, narrower terms, related terms and/or broader terms, which can be used to either further your search or refine the focus of your search.
Look up the topic being researched to discover possible alternative terminology by which to refine or expand your search. For example, a search for "antisocial personality disorder" (see Fig. 1) will retrieve a list of three main subject headings related to this topic (see Fig. 2), each of which have additional variant headings (see Fig 3).
Fig. 1
Fig. 2
Fig. 3
The "Scope Note" defines how this term is to be used.
Examine the Variants, Broader Terms, Narrower Terms, Related Terms and Closely Matching Concepts as well.
Select each term that looks promising to find additional terms to use to broaden your search and/or alternative terms to use to focus your search. The terms may even offer a different direction that you had not thought of.
If there is a U.S. Closely Matching Concept from another Scheme, click on it to see if it might be useful. Other schemes include MeSH, USDA National Agricultural Library.
In this instance, there is also a notification of an Earlier Established Form of the topic, which may be used as either a subject or keyword search to retrieve older resources for an historical analysis.
Last updated October, 2018.
For terms not found in LCSH or MeSH
Last updated February, 2021.
MeSH Headings provide a hierarchically-organized terminology for indexing and cataloging of biomedical information such as MEDLINE/PUBmed and other NLM databases. The MeSH Browser provides the search engine for identifying related MeSH Headings
A search for Antisocial Personality Disorder in the MeSH Browser reveals broader, narrower and related terms similar to the information provided in LCSH. 
Notice the more detailed definition in the Scope Note; the Entry Term(s), as well as Public MeSH Note, Online Note and History Note, which provides the terminological history of the concept. With this information you know that a search using "sociopathic personality" will likely give you resources that were published in the early '60's through the late '70's, whereas "antisocial personality" will cover resources from the mid-'70's to the early '80's. Anything published after that will need the phrase "antisocial personality disorder".
Be sure to examine the MeSH Tree Structure to understand how your selected term fits within the hierarchy of related concepts. 
Last updated February, 2021.