@Sweetpea while you can never be 100% sure, there are some rules of thumb.
In my experience people take drugs for two reasons, either to distract from or escape from reality or affect their mood. So depressant and stimulant use tracks more with mood disorders like Bipolar Disorder, whereas cannabis use and the like track with Psychotic disorders like Schizophrenia.
Both PTSD and SZA (the more common abbreviation for Schizoaffective Disorder) present with a mix both psychotic and mood symptoms, so the drug used may relate to the predominant symptom. PTSD is more transitory and trigger-based than SZA. Drug induced psychosis tends to fade as the drugs leave the system, but there’s evidence that prolonged drug use or even short term drug use by susceptible individuals can lead to more lasting issues or permanent damage.
What they generally look for is whether symptoms fade on their own, whether drugs are found in the patients’ system and how they respond to medication. The bottom line is she shouldn’t be taking illegal drugs regardless. While there may be some consolation in thinking that her issue is drug induced and possibly temporary, versus of seemingly permanent organic origin, I’m not sure it matters. She needs to stop using and keeping sober will be a life-long vigil. I don’t see much of a distinction between that and taking medication and getting psychiatric help instead or in addition.
One thing I’ll mention that I’ve had both psychiatrists and psychologists say to me. People should not get so hung up with chasing their tails with diagnoses. I went to a psychologist for a year and never once did she give me a DX. I ended up telling her what I thought I was, but she never said I was ‘right’.
My present Psychiatrist says that no one fits a DX perfectly that they might be PTSD-ish or SZ or SZA -ish or any mix or match. Insurance companies force doctors to put down a code and that can dictate what they pay, so the DX may change based on what insurance company the patient is filing a claim with and so on. I pay my psychiatric bills out of my HSA, because my psychiatrist like many nowadays refuses to deal with insurance company paperwork. I could file on my own, but isn’t much worth it. Because of this, he uses some medical code that I looked up that translates to Unknown Psychotic Disorder.