Current treatment of psychosis relies heavily on antipsychotics and rarely addresses the risk factors that have contributed to the onset and persistence of the psychosis. We consider that the best way to optimise research into, and personalise treatment of, psychosis is to attend to the causal risk factors. Acting on a background of polygenic susceptibility, the major types of environmental risk factors comprise neurodevelopmental hazards, drug abuse and social adversity. Unfortunately, research lumps together patients exposed to these different risk factors and, as a result, the neuropsychological or imaging characteristics associated with a particular environmental risk factor are obscured by being merged with patients with whom they have little in common aetiologically. A better strategy is to identify patients whose psychosis has resulted predominantly from exposure to one particular risk factor and then establish the pathway and characteristics associated with this risk. Thus, patients with neurodevelopmental impairment show an excess of premorbid abnormalities, prominent negative symptoms, cognitive and brain structural abnormalities and poorer outcome. Secondly, those patients whose psychosis results from drug abuse have largely normal premorbid social function and cognition and prominent positive symptoms. Thirdly, patients who have been exposed to social adversity often present with post-traumatic stress disorder (PTSD) symptoms or anxiety and depression as part of their psychosis. Appropriate interventions should be offered, in addition to antipsychotics, to patients in accord with their exposure to the different risk factors. For example, the patient who had been subject to child abuse should be offered trauma-based therapy, and antidepressants as appropriate, while the patient who continues to abuse cannabis should be offered cognitive behavioural therapy (CBT)/motivational therapy to decrease his/her drug consumption. Those patients who have been exposed to several risk factors deserve to have attention directed to each of these in turn.