ObjectivesEvaluate the association of adequate analgesia and time to analgesia with emergency department (ED) length of stay (LOS).Setting and DesignPost hoc analysis of real-time archived data.ParticipantsWe included all consecutive ED patients ≥18 years with pain intensity >6 (verbal numerical scale from 0 to 10), assigned to an ED bed, and whose pain was re-evaluated less than 1 h after receiving analgesic treatment.Outcome measuresThe main outcome was ED-LOS in patients who had adequate pain relief (AR=↓50% pain intensity) compared with those who did not have such relief (NR).ResultsA total of 2033 patients (mean age 49.5 years; 51% men) met our inclusion criteria; 58.3% were discharged, and 41.7% were admitted. Among patients discharged or admitted, there was no significant difference in ED-LOS between those with AR (median (25th–75th centile): 9.6 h (6.3–14.8) and 18.2 h (11.6–25.7), respectively) and NR (median (25th–75th centile): 9.6 h (6.6–16.0) and 17.4 h (11.3–26.5), respectively). After controlling for confounding factors, rapid time to analgesia (not AR) was associated with shorter ED-LOS of discharged and admitted patients (p<0.001 and <0.05, respectively). When adjusting for confounding variables, ED-LOS is shortened by 2 h (95% CI 1.1 to 2.8) when delay to receive analgesic is <90 min compared with >90 min for discharged and by 2.3 h (95% CI 0.17 to 4.4) for admitted patients.ConclusionsIn our study, AR was not linked with short ED-LOS. However, rapid administration of analgesia was associated with short ED-LOS.