Objective To compare the effects of metoclopramide and domperidone on the breast milk output of mothers with infants in neonatal intensive care.

Design Double-blind randomised controlled trial.

Setting Tertiary level neonatal intensive care unit (NICU).

Sample Eighty mothers expressing breast milk for their infants (mean gestational age 28 weeks) based in NICU and the amounts expressed fell short of the prescribed target.

Intervention Mothers were randomised to receive domperidone or metoclopramide for 10 days (10 mg three times a day).

Outcome measures Total milk volume daily for up to 10 days before the medication, 10 days during the trial and up to 10 days after medication. Adverse side effects were also recorded.

Results Mothers produced more milk in the domperidone group and achieved a mean of 96.3% increase in milk volume (mean increase/pretrial volume) compared with a 93.7% increase for metoclopramide. After adjusting for the amount of milk produced prior to medication, the mean amount of milk produced while taking medication for those on domperidone was 31.0 ml/24 h (95% CI −5.67 to 67.6) greater than the mean for those on metoclopramide. Seven mothers taking metoclopramide reported side effects and three taking domperidone; a further eight women (of 29) who had a follow-on prescription for metoclopramide also reported side effects.

Conclusions Oral domperidone and metoclopramide increased the volume of milk produced by mothers who are expressing to feed their babies in NICU. There were small differences in milk output between the two medications and in the incidence of side effects, but the differences were non-significant.