Abstract: While placebo-controlled studies continue to be required by regulatory authorities for the licensing of new drugs for schizophrenia to demonstrate maintenance of effect, the long-term risks to participants are largely unknown. We compared the response to treatment with paliperidone palmitate before and after relapse in such a study. This was a post-hoc analysis of 97 patients with schizophrenia who relapsed while receiving placebo in a multinational relapse prevention clinical trial. Patients underwent an initial open-label treatment phase of 33weeks (comprising a 9-week transition phase to switch patients to paliperidone palmitate, a 12-week flexible-dose phase and a 12-week fixed-dose phase); a double-blind phase of variable duration during which stabilized patients were randomized 1:1 to either continue paliperidone palmitate or receive placebo; and an optional 52-week open-label flexible-dose extension phase. There was a small but significant increase in PANSS total scores after eight months of treatment following relapse (56.7[12.68]) compared with prerelapse endpoint (54.5[11.74]) (p=0.026). Fourteen of 97 (14.4%) patients who had initially responded favorably to treatment met predefined nonresponse criteria in the postrelapse treatment phase, suggesting that treatment refractoriness may evolve in a subset of patients after relapse. However, relapses occurred in 18% of patients randomized to ongoing treatment in the double-blind phase, raising the possibility that treatment failure may also evolve in patients receiving continuous treatment. These findings may help inform decisions regarding the future of placebo-controlled trials in schizophrenia.