Prolonged elevation of hypothalamic opioid peptide activity in women taking oral contraceptives.

To examine the hypothesis that endogenous opioid peptide activity is chronically elevated by oral contraceptives, we infused either naloxone or saline into 10 women during the use of, or 5-6 and 9-10 days after stopping, combination birth control pills. A paradoxical increase in prolactin occurred with naloxone infusion during and 5-6 days after stopping the pills. Serum LH levels were not significantly elevated by naloxone until 9-10 days after cessation of pill use. These results suggest that hypothalamic opioid peptide activity is continuously elevated in women taking oral contraceptives.