Both the progestogen used and the dose of ethinylestradiol affect the venous thrombosis risk associated with combined oral contraceptive pills (COCPs), a systematic review and network meta-analysis has found. A total of 3,110 publications were retrieved of which only 25 publications reporting on 26 studies were included. Incidence of venous thrombosis in non-users from two cohorts was 1.9 and 3.7 per 10,000 woman-years which is consistent with previously reported rates of 1-6 per 10,000 woman-years. COCP use increased the venous thrombosis risk compared with non-use, relative risk (RR) 3.5, (95% CI:2.9 to 4.3). All preparations were associated with more than a two-fold increased risk of venous thrombosis compared with non-use. [With external links to the current evidence base]