 Despite different pharmacological properties, the scientific evidence is inconclusive regarding which of the first-line second generation antipsychotics SGAs should be preferred for the individual patient suffering from psychosis. The limitations of the evidence base may be related to the highly selected samples, short duration, and rigid experimental designs of most randomized clinical trials of efficacy. Moreover a high proportion of the clinical trials are drug company sponsored which could introduce funding bias. The purpose of this non-commercially funded study is to investigate whether effectiveness differences exist among the first-line SGAs olanzapine, quetiapine, risperidone, and ziprasidone when the drugs are used in a representative clinical setting. Eligible patients are those admitted to hospital for acute psychosis and candidates for oral antipsychotic treatment. The investigators hypothesise that in the naturalistic setting of every-day clinical practice and in a diverse sample representative of most patients admitted for symptoms of acute psychosis, differential effectiveness among the SGAs could be disclosed when the patients are followed for up to 2 years. This could deliver valuable information regarding which SGA should be the starting antipsychotic drug in order to facilitate the most beneficial outcome. 