Objective To examine breastfeeding experiences up to 6 weeks postpartum for mothers administered intranasal fentanyl, subcutaneous fentanyl or intramuscular pethidine for intrapartum analgesia. Design A secondary analysis was undertaken using the per-protocol dataset to examine the third phase of a larger randomised controlled trial. This phase of the study examined breastfeeding intention and experience from the first hour of birth to 6 weeks postpartum. Medical records were audited and women were contacted at 6 weeks postpartum to complete a telephone questionnaire. Setting Two maternity hospitals in South Australia. Participants Healthy women birthing at term received intranasal fentanyl (n=37), subcutaneous fentanyl (n=37), or intramuscular pethidine (n=35). Findings While maternal characteristics and birth outcomes were comparable between groups, women who received either intranasal fentanyl or subcutaneous fentanyl experienced fewer difficulties in establishing breastfeeding by 6 weeks postpartum when compared to intramuscular pethidine (p<0.01). Key conclusions Women who received fentanyl reported that their neonates had less difficulties establishing breastfeeding, compared to those who received pethidine. Therefore, for woman who intend to breastfeed, fentanyl should be the preferred opiate, for the relief of pain in labour. Implications for practice When providing education to women in relation to intrapartum pain relief it is important to consider the potential influence on breastfeeding experience. This research provides evidence that fentanyl is a suitable alternative to pethidine for women requesting parenteral analgesia in labour.