Background: Post-partum haemorrhage (PPH) is a common complication of labour. Objective: To assess the effectiveness of oxytocin in comparison to no treatment for the prevention of PPH. Selection criteria: Published and unpublished randomised controlled trials (RCTs) comparing systemic oxytocin to placebo or no intervention for the prevention of PPH were included. We did not apply language restrictions. Search Strategy: We identified RCTs from the Cochrane network meta-analysis on uterotonics for the prevention of PPH and updated the search via: Ovid MEDLINE, Embase via Ovid, Web of Science, CENTRAL, CINAHL Plus and clinicaltrials.gov. Data collection and analysis: An Individual participant data (IPD) meta-analysis. Main results: Of 14 eligible RCTs, four provided IPD (n=4,304; 51.7% received oxytocin and 48.4% received placebo or no intervention). Meta-analysis of IPD showed that oxytocin decreased the risk of PPH≥500 mL (aOR 0.59; 95% CI 0.46 to 0.74) and PPH≥1000 mL (aOR 0.51; 95%CI 0.32 to 0.80). Of ten RCTs that did not share data, seven met trustworthiness criteria while three did not. Trustworthy IPD and aggregate data from RCTs meeting trustworthiness criteria (n=6,003) showed that oxytocin significantly reduced the rate of PPH≥500 mL (aOR 0.53; 95%CI 0.45 to 0.62) and PPH≥1000 mL (aOR 0.59; 95%CI 0.48 to 0.71). Three RCTs not meeting trustworthiness criteria (n=1,027) reported a larger risk reduction of oxytocin for PPH≥500mL (aOR 0.37; 95%CI 0.03 to 4.03) and PPH≥1000mL (aOR 0.13; 95%CI 0.01 to 1.45). Conclusions : Prophylactic oxytocin reduces the risk of PPH≥500mL and PPH≥1000mL compared to no treatment. Studies not meeting trustworthiness criteria reported a larger effect, underlining the importance of integrity assessment in MA.