Résumé : This study determined the total magnesium concentration in the breast milk of mothers that were using oral, steroidal contraceptives during lactation. The study involved two groups of breast-feeding mothers that were receiving oral contraception, and a control group of 15 breast-feeding mothers that did not receive oral contraception. The first group received a daily combination pill (levonorgestrel 0.15 mg + ethinylestradiol 0.03 mg); the second group received a daily mini-pill (progestin-only pill, containing norethindrone 0.35 mg). The total magnesium concentrations of plasma and breast milk were determined before the start of contraception and after 30 days of contraception. The results showed that after 30 days of contraception, the contraceptive drugs had not significantly modified the total breast milk magnesium concentration (1.16 ± 0.11 mmol/L before treatment
versus 1.01 ± 0.12 mmol/L, in first group; 0.97 ± 0.16 mmol/L before contraception
versus 1.08 ± 0.11 mmol/L, in the second group). There were no significant changes in the total magnesium concentration in the breast milk of the control group after the 30 days. In addition, the oral, steroidal contraceptives (pill and mini-pill) did not affect the total magnesium concentration in the plasma of lactating mothers.