Causality assessment · Causality: well established

Tamoxifen and Venous thromboembolism: is the FAERS signal real?

n=112 co-reports · PRR 4.3 · ROR 4.4

A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.

Causality: well established

Tamoxifen ↔ Venous thromboembolism

n=112 co-reports · PRR 4.3 · ROR 4.4

Tamoxifen, an anti-oestrogen used for hormone-receptor-positive breast cancer, raises the risk of blood clots — deep vein thrombosis and pulmonary embolism — by altering the balance of clotting factors, and this class of effect is shared with oestrogens and other hormonal treatments. The risk appears during treatment, is greater around surgery and immobility, and is a recognised, labelled hazard. The 112 co-reports (PRR 4.3) reflect both the real effect and the large number of women taking tamoxifen.

Regulatory basis: tamoxifen prescribing information (venous thromboembolism and stroke warning). Randomized breast-cancer trials.

Bradford Hill viewpoint	Status	Note
Temporality (necessary)	met	Clots occur during treatment and risk falls after withdrawal
Strength	met	PRR 4 on a modest co-report count
Consistency	met	Reproduced across randomized breast-cancer trials
Specificity	met	A recognised tamoxifen/hormonal effect
Biological gradient	partial	Risk rises around surgery, immobility, and with age
Plausibility	met	Oestrogen-receptor modulation of clotting factors is the proposed mechanism
Coherence	met	Coheres with the labelled thromboembolism warning
Experiment	met	Randomized trials recorded thrombotic events by arm
Analogy	met	Analogous to VTE risk with oestrogens and other hormonal therapies

This page's own qualitative read, not an automated/citation-gated assessment.

✓ Trial evidence found — Triptorelin With Either Exemestane or Tamoxifen in Treating Premenopausal Women With Hormone-Responsive Breast Cancer (NCT00066703), N=2,638

Term (as recorded)	T+OFS (n=1321)	E+OFS (n=1317)
Thrombosis/embolism (vascular access-related) — Injury, poisoning and procedural complications	29	13

Serious vascular-access thrombosis/embolism occurred in 29 of 1,321 patients on tamoxifen versus 13 of 1,317 on exemestane in this randomized breast-cancer trial — a roughly two-fold excess, consistent with tamoxifen's established venous-thromboembolism risk. View on ClinicalTrials.gov →