The purpose of this study is to determine whether omega-3 fatty acids are effective in the prevention of psychosis in individuals at ultra-high risk for psychosis.

PURPOSE is a randomized double-blind placebo-controlled study. Main objective is to assess the effectivity of omega-3 fatty acid treatment in the prevention of psychosis. The primary outcome measure is the rate of transition to psychosis as determined through CAARMS. Subjects in the age range of 13-20 years with a higher chance of developing psychosis, as determined by the CAARMS, are treated for 6 months with omega-3 fatty acids or placebo. This study in conducted at 14 sites in 9 countries.

Inclusion Criteria:

• Written informed consent of the subject. For individuals younger than 18 years of age the parents / legal representatives need to give consent, and the subject can provide assent (whether the latter is required depends on local laws and regulations).
• UHR diagnosis as made using the Comprehensive Assessment of At-Risk Mental States (CAARMS) (Yung et al., 2005). Subjects have to meet one or more of the following criteria: (a) attenuated psychotic symptoms, (b) brief limited intermittent psychotic symptoms (a history of one or more episodes of frank psychotic symptoms that resolved spontaneously within 1 week in the past year), or (c) either the presence of schizotypal personality disorder or a family history of psychosis in a first-degree relative, all three together with a recent decline in function.

Exclusion Criteria:

• Any clinically significant medical condition that may influence the results of the trial or affect the ability to take part in a trial.
• Laboratory screening values considered clinically relevant by a medical doctor for transaminases, thyroid hormones or coagulation parameters
• Current or past DSM-IV diagnosis of psychosis, as measured with K-SADS-PL
• Current treatment with an antipsychotic or mood-stabilising agent
• Intake of an antipsychotic or mood-stabilising agent in the two weeks prior to study inclusion
• Intake of an antipsychotic agent equivalent to a total haloperidol use of >50 mg in the six months prior to study inclusion
• A first-degree relative (i.e. parents, offspring or siblings) participating in this study
• UHR diagnosis on the basis of attenuated psychotic symptoms that are entirely explained by acute intoxication
• Current aggression or dangerous behaviour (PANSS G14 score 5 or above)
• Current suicidality / self-harm (PANSS G6 score 7)
• Current DSM-IV diagnosis of alcohol or substance dependence as measured with K-SADS-PL
• Any current or previous neurological disorder, including epilepsy
• History of head injury resulting in unconsciousness lasting at least 1 hour
• IQ < 70
• More than 4 weeks of regular omega-3 supplementation (>2 daily capsules standard strength providing >600 mg combined EPA/DHA) within the last 6 months.