Subanalyses among extreme metabolizers showed similar results (CTG: HR, 0.99; 95% CI, 0.48-2.03; SCM: HR, 0.93; 95% CI, 0.44-1.96).<h4>Conclusions and relevance</h4>The results of this randomized clinical trial do not support routine CYP testing in patients with schizophrenia.<h4>Trial registration</h4>ClinicalTrials.gov Identifier: NCT00707382. Here, PPIG is linked to schizophrenia.