The goal of this observational study is to the early impacts of psychosis and antipsychotic medications on brain metabolism in young adults recently diagnosed with a first episode of psychosis.

The main question aims to evaluate the effect of 4 to 6 weeks of antipsychotic medication on brain metabolism measured by PET scan (cerebral uptake of 11C-Acetoacetate + 18 Fluorodeoxyglucose).

Participants will undergo a multimodal imaging protocol with other measures of psychopathology (e.g., cognition, depressive symptoms, etc.) and (metabolic marker, inflammation, etc).

Inclusion Criteria:

• Admission to the PEP clinic in Estrie, either outpatient or inpatient, according to the transdiagnostic PEP model.
• Willingness to begin taking an AP (regardless of type and dose, or change in type and dose during the study).
• Ability to read and express themselves in French or English.
• Capable of understanding and signing consent.

Exclusion Criteria:

• Pregnancy, childbirth in the last 6 months, or breastfeeding.
• Presence of a metallic object in the body that is incompatible with MRI.
• Any use of APs for more than 2 continuous weeks in the past year and/or 6 weeks in a lifetime (except for aripiprazole if taken at less than 2.5 mg/day or quetiapine at less than 50 mg/day, regardless of duration or timing of the prescription).
• The following comorbidities: psychosis + borderline or intellectual disability, autism spectrum disorder, substance use disorder with decompensation, psychosis induced by a medical condition, or psychosis induced by drug use or withdrawal.
• Type 1 diabetes.
• Uncontrolled acute suicidal ideation.
• Other conditions that could interfere with participation according to the judgment of the qualified physician.

Individuals aged 18 to 35 from the Estrie region who have been evaluated by the PEP team and wish to start an antipsychotic (AP) for the treatment of a first episode of psychosis.