Effect of oral contraceptives on serum prolactin: a longitudinal study in 126 normal premenopausal women.

A prospective longitudinal study was carried out in 126 normal premenopausal women aged 18-34 years to determine the effect of oral contraceptives containing less than 50 micrograms of oestrogen on serum prolactin concentration. The mean prolactin concentration in patients receiving oral contraceptives (n = 80) rose from a control level of 8.9 ng/ml to 10.2 ng/ml at 3 months (P less than 0.05) and 10.9 ng/ml at 12 months (P less than 0.001). In a parallel group of patients (n = 46) who used intrauterine devices for contraception, no significant change in serum prolactin concentration was observed over the same period. It is concluded that currently available oral contraceptives have a small but significant stimulatory effect on prolactin secretion in normal women.