I see your profile is the USA here is what the USA goes by (and most of the world now since all but a small few now use the DSM 5 standards)...

Criterion H (required): Symptoms are not due to medication, substance use, or other illness.

you can find this here https://www.ptsd.va.gov/professional...teria_ptsd.asp

or by visiting your local library reference department. they will be able to show you what the diagnostic criteria in your location is for PTSD since 2013.