Clozapine is the most effective antipsychotic for the 25% to 33% of people with schizophrenia who are treatment resistant, but not all people achieve response. Using data from a previously published clozapine systematic review and meta-analysis, we explored the proportion of people who achieved response and examined the absolute and percentage change in Positive and Negative Syndrome Scale (PANSS) scores. Overall, 40.1% (95% confidence interval [CI], 36.8%-43.4%) responded, with a mean reduction in PANSS of 22.0 points (95% CI, 20.9-23.1), a reduction of 25.8% (95% CI, 24.7%-26.9%) from baseline. These reductions are clinically meaningful. A 40% response rate to clozapine suggests that 12% to 20% of people with schizophrenia will be ultra-resistant.