Data on immune reconstitution inflammatory syndrome (IRIS), despite being a widely recognized complication of antiretroviral therapy, remain limited. The objective of the present study was to evaluate the time-to-onset and factors affecting clinical outcomes of IRIS in people living with HIV (PLWH) using data from the Japanese Adverse Drug Event Report (JADER) database. Data of PLWH who developed IRIS as an adverse event were extracted from the JADER database. Cases with the data of both the start date of anti-HIV drug therapy and date of IRIS onset were included in the study. The survey items included sex, age, anti-HIV drug use, IRIS-compatible events, time-to-onset of IRIS, and clinical outcome. The time-to-onset of IRIS was evaluated in relation to anchor drug use. Overall, 79 cases were included in the analysis. The median (range) time-to-onset of IRIS was 29 (1-365) days, and it differed significantly between IRIS-compatible events (P = 0.029). In particular, the time-to-onset of Pneumocystis pneumonia-IRIS was the shortest among the IRIS-compatible events (median [range]: 12 [5-301] days). Age ≥ 50 years at IRIS onset appeared to be related to the poor clinical outcomes of IRIS in PLWH (P = 0.048). The use of integrase strand transfer inhibitors did not affect the time-to-onset of IRIS or clinical outcome of IRIS in PLWH. This analysis based on the data from the JADER database revealed that IRIS-compatible events were related to the time-to-onset of IRIS and that patients older than 50 years had poorer clinical outcomes of IRIS. This finding will be useful for healthcare professionals when considering medications for patients with HIV infection/AIDS and for the management of IRIS.