<qa>  What is the CYP1A2 isoenzyme?While levels of caffeine consumption are considered to be high in the general population, there is some evidence that they may be even higher within schizophrenia SZ patients. In a recent U.S. study of 146 community-dwelling individuals with SZ, daily consumption rates of caffeine were nearly double those observed in a healthy control population 471.6 mgday vs. 254.2 mgday; p .001. Furthermore, 13 of the SZ population studied ingested more than 1000 mgday of caffeine, with the highest observed intake at 2647.2 mgday. To place this in context, Health Canada recommends adults consume no more than 400 mg of caffeine per day, and doses above 250 mg have the potential to induce symptoms of anxiety, agitation, irritability and insomnia . High doses of caffeine are particularly concerning for individuals with SZ as caffeine alters dopaminergic activity at post-synaptic neurons through its actions at adenosine A2A receptors; this enhances dopamine function, resulting in increased locomotor activity and appears to exacerbate positive symptoms, such as delusions and hallucinations . Another effect of caffeine with particular relevance to SZ involves its interaction with atypical antipsychotic drugs, such as clozapine. Both clozapine and caffeine are metabolized in the liver by the cytochrome P450 system and, in particular, the CYP1A2 isoenzyme. Competition between clozapine and caffeine has been reported to elevate antipsychotic blood levels, increasing the risk of clinically significant side effects at high dosage levels of caffeine. As such, given the high consumption levels and potential negative side effects of caffeine in SZ, it is important to understand the cortical mechanisms that underlie caffeine use. 