BACKGROUND: A rise in the concentration of oxytocin causes contraction of cells around the alveoli and milk ducts, in preparation for suckling. Lactation failure may result from insufficient oxytocin. OBJECTIVES: The objective of this review was to assess the effects of using oral or nasal oxytocin on lactation. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register. SELECTION CRITERIA: Randomised and quasi-randomised trials of variable doses of oxytocin and different methods of administration versus placebo in breastfeeding women using oxytocin to augment lactation. DATA COLLECTION AND ANALYSIS: Trial quality was assessed and data were extracted by two reviewers. MAIN RESULTS: Four trials of 639 women were included. There was potential for significant bias in these trials. Restricted breastfeeding schedules may have contributed to inadequate production of milk by the participants. Sublingual and buccal preparations of oxytocin were associated with an increase in milk production. Oxytocin did not appear to increase the incidence of breast pain and 100 international units of oxytocin appeared to be slightly more beneficial than 10 international units. REVIEWER'S CONCLUSIONS: An appropriate dose of sublingual or buccal oxytocin may help augment lactation where necessary. However if women are encouraged and supported with unrestricted breastfeeding, the need for oxytocin would probably be diminished.