Background: Increased risk of venous thromboembolism (VTE) is a life-threatening side effect for users of oral contraceptives (OCs) or hormone therapy (HT).

Objectives: To investigate the potential for genetic predisposition to VTE in OC or HT users, we conducted a gene-by-environment case-only meta-analysis of genome-wide association studies (GWAS).

Methods: Use or nonuse of OCs (7 studies) or HT (8 studies) at the time of the VTE event was determined by pharmacy records or self-report. A synergy index (SI) was modeled for each variant in each study and submultiplicative/supramultiplicative gene-by-environment interactions were estimated. The SI parameters were first meta-analyzed across OC and HT studies and subsequently meta-analyzed to obtain an overall estimate. The primary analysis was agnostic GWAS and interrogated all imputed genotypes using a P value threshold of <5.0 × 10^-8; secondary analyses were candidate-based.

Results: The VTE case-only OC meta-analysis included 2895 OC users and 6607 nonusers; the case-only HT meta-analysis included 2434 HT users and 12 793 nonusers. In primary GWAS meta-analyses, no variant reached genome-wide significance, but the smallest P value approached statistical significance: rs9386463 (P = 5.03 × 10^-8). We tested associations for 138 candidate variants and identified 2 that exceeded statistical significance (0.05/138 = 3.62 × 10^-4): F5 rs6025 (P = 1.87 × 10^-5; SI, 1.29; previously observed) and F11 rs2036914 (P = 2.0 × 10^-4; SI, 0.91; new observation).

Conclusion: The candidate variant approach to identify submultiplictive/supramultiplicative associations between genetic variation and OC and HT use identified a new association with common genetic variation in F11, while the agnostic interrogations did not yield new discoveries.