For more information see section 3.11 in the AMA Manual of Style, 11th ed.
Journal titles should use standard abbreviations of the National Library of Medicine (NLM) Catalog. Search the NLM Catalog.
Prefer DOIs to URLs when available. No access date is needed for DOIs, but an access date is needed for URLs. Neither DOIs nor URLs should be followed with a period.
If you can't find the DOI for an article, you can use a DOI lookup tool.
For formatting for multiple authors and group authors, see the author name guidelines.
Author(s). Title of article. Abbreviated Journal Name. Year;vol(issue):inclusive pages. doi:xx.xxxx OR Accessed [date]. URL
An example of an article without a DOI is included,4 but such citations should be increasingly rare as even older articles are being assigned DOIs.
Preprints are articles released before formal publication, therefore usually before peer-review. If a preprint is later published in a peer-reviewed journal, it can be cited using the normal AMA journal citation. However, according to the AMA manual, "The version cited should be the version used."
The example below is the same article in preprint5 and published in a peer-reviewed journal.6 As you can see, information like the title may change in the publication process.