Lower reporting of venous thromboembolisms events with natural estrogen-based combined oral contraceptives compared to ethinylestradiol-containing pills: A disproportionality analysis of the Eudravigilance Database

Objectives: Pharmacovigilance data analysis can accelerate the identification of drug-related safety signals or reassure on the safety profile. This study evaluates the venous thromboembolism (VTE) risk of newer combined oral contraceptive (COC) formulations with natural estrogens, such as estradiol (E2) and estetrol (E4), using data from the EudraVigilance database. Study design: We conducted a disproportionality reporting rate analysis of VTE events associated with various COC formulations by extracting individual case reports from EudraVigilance database up to July 28, 2024. The study compared the proportionality reporting rate between natural estrogen-based COCs (E2 and E4) and conventional synthetic estrogen-based COCs (ethinylestradiol [EE]), with a comparison to EE-levonorgestrel. Results: The analysis revealed that COCs containing natural estrogens exhibited significantly lower proportionality reporting rates for thrombotic events compared to EE-based COCs. Specifically, E4-drospirenone (E4-DRSP) showed the lowest proportionality reporting rate (0.12), similar to progestin-only pills. EE-DRSP had the highest proportionality reporting rate (2.25), suggesting an increased thrombotic risk. Conclusions: The study supports the safer thrombotic profile of natural estrogen-based COCs, particularly E2 and E4 formulations, over synthetic estrogen-based COCs containing EE. These findings support the hypothesis that E2- and E4-based pills are safer than EE-based pills, aligning with a shift toward safer contraceptive options in clinical practice. Implications: Natural estrogens such as E2 and E4 may emerge as safer alternatives to synthetic estrogens like EE, particularly when combined with progestins like DRSP. This multilevel evidence underscores the importance of evidence-based prescribing practices to enhance patient safety and minimize thrombotic risks associated with COC use.