In fact, there are many causes of psychoses besides schizophrenia.  Of course, severe cases of bipolar disorder or severe depression can have psychotic features.  But many patients suffer schizophrenic-like illnesses due to brain damage from specific causes, but we just can't tell what has caused the psychosis.  However, if the person has suffered brain damage due to marijuana or other drug abuse or due to head trauma or past infection, the treatment is pretty much the same and nothing is going to cure the brain damage.  

Still, there are cases, especially where the psychosis is of sudden onset, where medications of various types are causing the psychosis.  These are usually readily apparent and simply stopping the medication resolves the problem.  Sometimes, the diagnosis is not so easy.  Even psychiatric medications, primarily anti-depressants, can in rare instances cause psychosis.  It is important to be alert to the possibilities and let your physician know as much as possible including herbal remedies, etc.  Below are just a few examples of such reactions.

Psychosis: High Anticardiolipin Antibodies: 34 patients, not medicated on admission, were compared to controls. 32% had anti-phospholipid antibodies. 24% had aCL anti-cardiolipic antibodies and 9% lupus anti-coagulant anti-phospholipid antibodies. They are auto-antibodies with a high affinity to negatively charged phospholipids in the inner surface of the cell membrane and may play a causal role although there is no evidence for this at the moment. M. Schwartz, Heifa, J Clin Psychiatry 1/98 59:20-23

Psychosis Case: Celecoxib Auditory Hallucination: A case of a 78yo man is reported where after 2 days on medication he started hearing voices. Other non-steroidal anti-inflammatory medications can also cause psychiatric effects. AJP 00;157:1022

Psychosis Case: Topical Ciprofloxacin Eye Drops: A case of auditory hallucinations, irrational conversation, acute psychosis after 3 days of Cipro eye-drops. The psychosis resolved in 26 hours after stopping the drops. There are similar reports with oral Cipro. Arch Ophthal 02;120:665

Psychosis Cases: Metoclopramide Withdrawal Psychosis: Two cases are reported of men over 65 years old on 20mg/d of metoclopramide (Reglan) for GI disorders. Both developed psychotic symptoms (hallucinations, and delusions) in 12-72 hr after stopping the medicine. Both did well with risperidone 1mg/d which was able to be tapered and stopped after 5-6 weeks.

Psychosis Cases: Mefloquine Psychosis & Suicide: The antimalaria mefloquine (Lariam) can cause anxiety, hallucinations, nightmares, psychosis and cases of suicide. WSJ 9/4/02