Objectives: This study aimed to estimate the prevalence of psychoactive substance (PAS) use in night-shift healthcare workers (NSHW) during France's first COVID-19 wave (March-May 2020).Design: Observational cross-sectional online survey.Setting: 39 public hospitals in the Assitance Publique des Hôpitaux de Paris (AP-HP) network in the Parisian area.Participants: A total of 1238 nurses, assistant nurses, X-ray technicians, managers, lab technicians, midwives and childcare assistants working at night or alternating between days and nights answered the questionnaire.Intervention: Online survey.Outcome measures: PAS use prevalence after weighting data for sex, age and profession using calibration on margins, in order to be representative of al...