Background: ŚÁ₁-Adrenoceptor blockers (ŚÁ1Bs) are used for the treatment of benign prostatic hyperplasia and hypertension, but they are known to cause hypotension-related adverse events. The objective of the present study was to evaluate the onset time profiles for syncope associated with the use of ŚÁ1Bs. Methods: We analyzed the data obtained from the Japanese Adverse Drug Event Report (JADER) database for a period from April 2004 until November 2016 and calculated reporting odds ratios (RORs) for eight ŚÁ1Bs available on the Japanese market, using disproportionality analysis. Moreover, time information recorded in the JADER database was analyzed to evaluate the onset times of adverse events. Results: In total, 186,724 reports for males older than 20 years were analyzed. Significant RORs for syncope, with 95% confidence intervals, were obtained for naftopidil (2.53, 1.81 - 3.53), silodosin (4.24, 2.37 - 5.20), and tamsulosin (2.22, 1.75 - 2.81). The median onset times of syncope for naftopidil, silodosin, and tamsulosin were 37, 26, and 108 days, respectively. The shape parameters obtained by fitting the data for the three ŚÁ1Bs to the Weibull distribution were all less than 1.0, indicating that all these drugs could be classified as the early failure type. The cumulative incidence rates showed that the onset times of syncope tended to be similar among the three ŚÁ1Bs.