Brain dynamics predict oral contraceptive treatment duration

Oral contraceptives are used by millions of women worldwide, yet their cumulative effects on the female brain remain poorly understood. We analyzed resting-state fMRI from 192 women (never, current, and past users) using brain-dynamics metrics that quantify information transfer across spatiotemporal scales. Duration of use was associated with a progressive, age-independent modulation of brain dynamics: prolonged use was related to restricted local synchronization but enhanced information flow across scales. Machine learning predicted individual duration of use from brain dynamics, and node-level classifiers distinguished users from never-users based on a spatially distributed cortical pattern spanning multiple functional networks, most clearly detectable in long-term users. In past users, these associations were inverted in sign, scaling with prior duration rather than returning to the never-user baseline, suggesting active reorganization following cessation. Together, these results indicate that cumulative oral contraceptive exposure acts as a neuromodulator of information processing.