Do infant formula samples shorten the duration of breast-feeding?

To determine whether advertising by infant formula companies shortens the duration of breast-feeding, we randomly assigned 448 breast-feeding new mothers to either receive or not receive a formula sample packet upon discharge from a maternity ward. These mother, unaware of the study, were then telephoned 3 months post partum by a research assistant blind to the randomisation status. "Sample" mothers were less likely to still be breast-feeding at 1 month (78% vs 84%, p = 0.07) and more likely to have introduced solid foods by 2 months (18% vs 10%, p = 0.01). These trends became more significant in three vulnerable subgroups: less educated mothers, primiparas, and mothers who had been ill post partum. Our results suggest that infant formula samples may shorten the duration of breast-feeding and hasten the age at which solids are introduced.