Background: The effectiveness of glucocorticoids in preventing biphasic reactions in patients with anaphylaxis is still controversial. We evaluated the effects of glucocorticoids on rates of biphasic reactions in patients with anaphylaxis treated with adrenaline. Methods: In this retrospective observational study using a national inpatient database in Japan, we identified 31,570 patients with anaphylaxis treated with adrenaline on the day of admission. We divided them into two groups: those who were treated with adrenaline plus glucocorticoids and those who received adrenaline only on the day of admission. We performed a one-to-four propensity score matching analysis between the two groups. The primary outcome was occurrence of a biphasic reaction and the secondary outcome was 7-day all-cause mortality. Results: Of the 31,570 eligible patients, 28,145 (89.2%) were treated with glucocorticoids. After propensity score matching, there were no significant differences in rates of biphasic reactions (odds ratio, 1.03; 95% confidence interval, 0.86–1.24; p=0.14) or 7-day all-cause mortality (odds ratio, 0.68; 95% confidence interval, 0.40–1.17; p=0.16) between patients with anaphylaxis treated with and without glucocorticoids. Conclusion: Our findings do not support the use of glucocorticoids to prevent biphasic reactions in patients with severe anaphylaxis requiring adrenaline.