The overall goal of this study is to determine the efficacy and tolerability of three atypical antipsychotic medications (risperidone, olanzapine, and quetiapine) in the treatment of adolescents with psychosis. It is hypothesized that the three medications will be equally effective in reducing the symptoms of psychosis.

The purpose of this study is to compare the efficacy and tolerance of three atypical antipsychotics, which are medications that have been in use for about the last 10 years, in the treatment of psychosis in adolescents. Efficacy refers to how well the medications work in decreasing symptoms associated with schizophrenia, and tolerance refers to the level of side effects and the compliance with taking the medications. All three medications have demonstrated efficacy in treating psychosis without causing extra pyramidal side effects (uncontrolled muscle movements) that are associated with typical, or older antipsychotic medications. Young people may be at a greater risk for side effects from the typical antipsychotic medications. There are studies of the efficacy and tolerance among patients under 18-years-old taking the three drugs in this study: risperidone, olanzapine, and quetiapine. However, at this time there is little data available comparing these three medications. This study is an open-label, random assignment, 12-week study to assess the efficacy and tolerance of these three atypical antipsychotic medications in the treatment of adolescents (ages 12-18) with schizophrenia or psychosis. The participants will be informed of which medication she/he is taking, and will be assigned to the medication randomly (based on chance rather than choice).

There are additional theoretical beliefs in regard to this study as well. A secondary hypothesis of this study is that quetiapine will have less extra pyramidal side effects (EPS) and less prolactin-related side effects than risperidone. A third hypothesis is that quetiapine will lead to less weight gain than olanzapine and risperidone. Finally, it is hypothesized that because of the fewer side effects, quetiapine will be better tolerated than risperidone and olanzapine.

Inclusion Criteria:

1. Subjects are between the ages of 12-18 and have a diagnosis of a psychotic illness.
2. Subject currently meets criteria for one of the following disorders: schizophrenia, schizoaffective disorder (mainly schizophrenic), schizophreniform disorder, and psychosis NOS.
3. Subject is in good physical health and not suffering from any medical disorder that might mimic psychosis or lead to medical difficulty with the study medications.
4. If subject is taking antipsychotic medication before study entry, their medicine will be discontinued for 1-4 days depending on symptoms.

Exclusion Criteria:

1. Subject has a medical disorders that would interfere with the study, such as epilepsy, thyroid disease, liver disease, AIDS, etc.
2. Subject currently has substance dependence.
3. Subject is talking a medication that inhibits or induces the cytochrome P450 3A4 (specific medications listed in Appendix of protocol).

3. Subject meets criteria for brief psychosis or mood disorder with psychotic features.

4. Female subject is pregnant or nursing.