Low-mass X-ray binaries are systems in which a star transfers matter onto a compact object—either a black hole or a neutron star—producing energetic outbursts. During these events, their optical spectra provide a way to study extreme processes of accretion and matter ejection. While some spectroscopic features have been analysed in detail (e.g., revealing disc expansion and the presence of optical winds), the appearance of broad absorptions in the optical regime has traditionally been neglected. In this work, we present the first systematic study of these broad absorptions. We carry out the