Is it appropriate to treat people at high-risk of psychosis before first onset? - No

Schizophrenia expert David Castle suggests caution, especially regarding medication use

It has been suggested that one can “predict” schizophrenia at an individual level. Features posited as being part of these so-called ultra-high risk (UHR) criteria1 include risk factors (eg, a family history of schizophrenia), symptoms (eg, attenuated positive psychotic symptoms) and longitudinal trajectory (decline in functioning). Added to this, mostly, is the requirement that the individual be “help-seeking”, though this is a loose term and raises questions about pathways to care.