The aim of the present study is to assess the availability of cannabinoid receptors (CB1R) in the human brain. CB1R are present in everyone's brain, regardless of whether or not someone has used cannabis. The investigators will image brain cannabinoid receptors using Positron Emission Tomography (PET) imaging and the radioligand OMAR, in healthy individuals and several conditions including 1) cannabis use disorders, 2) psychotic disorders, 3) prodrome of psychotic illness and 4) individuals with a family history of alcoholism, 5) Post-Traumatic Stress Disorder 6) Opioid Use Disorder using the PET imaging agent or radiotracer, [11C]OMAR. This will allow us to characterize the number and distribution of CB1R in these conditions. It is likely that the list of conditions will be expanded after the collection of pilot data and as new data on cannabinoids receptor function and psychiatric disorders becomes available.

Those in the cannabis us disorder arm of the study will have a PET scan on at least three occasions: once while smoking as usual, once after 48-hours of abstinence from cannabis, and a final time after 4 weeks of abstinence. Additional scans may be conducted within the 4 weeks and the last scan may be conducted well beyond 4 weeks. Similarly, while most schizophrenia patients may get scanned just once, a subgroup of patients may get scanned more than once. For example to tease out the effects of medications, unmedicated patients may get scanned while unmedicated and again after treatment with antipsychotic medications. Similarly prodromes may get scanned while in the prodromal stage off medications, on medications and after conversion to schizophrenia.

Inclusion Criteria:

• Males ages 18-55
• For cannabis users:
• Willing to abstain from cannabis use for four weeks
• For schizophrenia:
• Meets DSM-IV-TR criteria for schizophrenia or schizoaffective disorder
• For prodrome for psychotic illness:
• Meets SIPS criteria for prodromal syndrome
• For family history positive:
• First degree relative with alcoholism
• For Post-Traumatic Stress Disorder
• Meets DSM-IV-TR criteria for PTSD
• For OUD
• Meets DSM-IV-TR criteria for Opioid Use Disorder

Exclusion Criteria:

• Current neuro-psychiatric illness (including cannabis dependence) or severe systemic disease. Cannabis use disorder is permitted in the cannabis dependent group. Schizophrenia and schizoaffective disorder is permitted in the schizophrenia group. Psychotic symptoms are permitted in the prodromal group. Post-Traumatic Stress Disorder is permitted in the PTSD group and Opioid Use Disorder is permitted in the OUD group.
• Presence of ferromagnetic metal in the body or heart pacemaker
• Have had exposure to ionizing radiation that in combination with the study tracer would result in a cumulative exposure that exceeds recommended exposure limits
• Are claustrophobic

The study population is composed of schizophrenia, cannabis dependence, prodromal for psychotic illness, family history of alcoholism, healthy volunteers, Post-Traumatic Stress Disorder and Opioid Use Disorder.