There are no FDA approved medications in the U.S. to augment lactation. Metoclopramide is used off-label but can have intolerable side effects. We examined the biological activity and safety of recombinant human prolactin (r-hPRL) as preliminary data for its use to augment lactation. Healthy, non-postpartum women (n=21) with regular menstrual cycles underwent a 7 day randomized, double-blind, placebo-controlled trial of r-hPRL. Galactorrhea, markers of bone turnover, calcium homeostasis and gonadal function were measured and side effects recorded.