Evidence is conflicting with regard to the comparative frequency of venous thrombolic events (VTE) among women using the transdermal patch when compared to an oral contraceptive (OC), even though the patch produces a relatively high serum ethinyl estradiol (EE) level (strength of recommendation [SOR]: C, conflicting cohort case-control studies). The vaginal ring has a risk of VTE comparable to that of an OC (SOR: B, 1 comparative study)
