Multinational, comparative, prospective, active surveillance study that follows two cohorts. The primary objective of the study is to characterize and compare the risks of E4/Drospirenone (DRSP) with levonorgestrel-containing combined oral contraceptives (EE/LNG) in a study population that is representative of the actual users of these preparations. The main clinical outcome of interest is venous thromboembolism (VTE), specifically deep venous thrombosis (DVT) and pulmonary embolism (PE). Secondary objectives include measuring the occurrence of unintended pregnancy, assessing the risk of arterial thromboembolism (ATE), describing the drug utilization pattern, describing the baseline risk profile for VTE and ATE, and investigating outcomes associated with foetal exposure to E4/DRSP.