The aim of this study was to compare the benefits and hemodynamic side effects of oxytocin between intravenous infusion with and without a bolus injection during a caesarean section. Women with singleton pregnancies who underwent caesarean sections under spinal anaesthesia were included. Oxytocin was administered by an iv bolus injection (5 U) followed by an intravenous infusion (10 U of oxytocin in 500 mL normal saline); this was switched to just an intravenous infusion. The amount of blood loss did not differ between the groups. In a multivariate analysis, the adjusted odds ratios for the risk of hypotension (≥20% reduction of systolic BP) and tachycardia (heart rate ≥100 bpm) were 4.5 (95% confidence interval [CI], 1.6-12.5) and 3.7 (95%CI 1.9-7.2) in the iv bolus group, respectively, compared with the just the infusion group. The oxytocin administration by iv bolus injection did not decrease blood loss and increased the rate of hemodynamic side effects.Impact statementWhat is already known on this subject? Oxytocin is used as the first-line uterotonic treatment to prevent a postpartum haemorrhage in women undergoing Caesarean Sections. Oxytocin is known to relax vascular smooth muscle, which can cause hypotension and tachycardia. The protocols for administering oxytocin during CS vary by institution.What do the results of this study add? Combined treatment with oxytocin by iv bolus injection (5 U) followed by iv infusion (10 U of oxytocin in 500 mL normal saline) during CS increased the risk of developing adverse hemodynamic side effects, including hypotension, tachycardia, and the need for vasopressors, without any benefit in the control of intraoperative blood loss in comparison to iv infusion alone.What are the implications of these findings for clinical practice and/or further research? We should abandon the iv bolus injection of oxytocin during CS, especially for women undergoing an elective CS who are not in labour.