Q. How do I reference DSM-5?

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) ...