The aims of this study are to compare the antipsychotic and adverse events of quetiapine, an atypical antipsychotic drug, to haloperidol, a standard treatment for primary psychotic disorder, in individuals with MAP.

Eighty individuals with MAP will be randomly assigned into two treatment groups, i.e. treatment with quetiapine and haloperidol. The quetiapine group will receive quetiapine at least 100 mg per day and the haloperidol group will receive haloperidol at least 2 mg per day orally once a day for four weeks. The doses will be increased every 5 days until no psychotic symptom is observed from the Positive and Negative Syndrome Scale. Common antipsychotic adverse events will be checked and documented daily.

Inclusion Criteria:

• Having a psychotic episode with current use of methamphetamine
• Positive urine toxicology test for methamphetamine on the first day of hospitalization

Exclusion Criteria:

• Using other illegal substances
• Having a history of primary psychotic disorders or using antipsychotic agents
• Having a chronic medical disease, e.g. essential hypertension, diabetes, epilepsy, stroke