This reference for DSM-5 is in the Harvard format:
Reference list: American Psychiatric Association (2013) Diagnostic and statistical manual of mental disorders: DSM-5. 5th edn. Washington, D.C.: American Psychiatric Publishing.
In-text citation (depending on sentence layout):
...(American Psychiatric Association, 2013).
American Psychiatric Association (2013) ...
This reference for DSM-5 in in the APA format:
Reference list: American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.).
Parenthetical citation: (American Psychiatric Association, 2013)
Narrative citation: American Psychiatric Association (2013)
N.B. This FAQ relates to the version of DSM-5 that is available to borrow from The Hive in Worcester.