Many journals require the use of Index Medicus/NLM format journal title abbreviations in the reference list. JAMA and other AMA citation style-using journals are included among those using these journal title abbreviations. These abbreviations are available through PubMed's Journals Referenced in NCBI Databases search tool.
To use this tool most efficiently, enter the journal title in quotes. For instance to search for an abbreviation for New England Journal of Medicine, search for
"New England Journal of Medicine"
Browse down the list of results to find the desired journal and abbreviation as shown in the figure below: