A case where two risks multiply rather than add. Estrogen raises clot risk on its own; in someone who also carries a thrombophilia variant the two compound.
Estrogen-containing contraception raises venous clot risk on its own, and in someone who also carries factor V Leiden the two effects multiply rather than simply add, producing a substantially higher risk than either factor alone. US CDC Medical Eligibility Criteria place combined hormonal contraceptives in category 4 — an unacceptable health risk — for people with a known thrombogenic mutation such as factor V Leiden. The same guidance states that routine screening for these mutations before starting contraception is not recommended, and the wider thrombophilia-screening literature gives the reason: the variant is uncommon and screening everyone yields little benefit for its cost. This is background information about a documented gene-drug interaction. It is not a recommendation to start, stop or switch any contraceptive; that decision belongs with your clinician.
CDC US Medical Eligibility Criteria for Contraceptive Use — combined hormonal contraceptives, thrombogenic mutations (category 4). PharmGKB/ClinPGx carries a clinical annotation for the F5 variant with hormonal contraceptives (evidence level 2A); there is no CPIC prescribing guideline for F5. Background evidence: Mohllajee AP et al., systematic review of hormonal contraceptive use in women with thrombogenic mutations, Contraception 2006, PMID 16413847.
These are the positions in your own file that carry the genes above. Not every gene in a guideline is one we report — where that is the case the gene appears above without a variant here, and the note says so.