Research

Hormonal

The combination of oral estrogen use with prothrombotic mutations (Factor V Leiden or Prothrombin G20210A) or obesity significantly enhances the risk of venous thromboembolism.

If you have a known blood clotting mutation (like Factor V Leiden) or are overweight/obese, taking oral estrogen significantly increases your risk of blood clots (up to 8 times higher for mutations). However, using transdermal estrogen (patches/gels) does not appear to add extra risk for these high-risk groups, making it a safer choice to discuss with your doctor.

StrongSupportsHIGH confidence
The combination of oral oestrogen and thrombogenic mutations or obesity further enhanced the risk of venous thromboembolism... odds ratio 8.0, 5.4 to 11.9... combination of current oral oestrogen use and an increased body mass index resulted in a further increase in the risk of venous thromboembolism (pooled odds ratio 5.4, 2.9 to 10.0)
Marianne Canonico et al. · BMJ · 2008

Why this rating

Meta-analysis of multiple case-control studies and RCTs (WHI).

Source

Hormone replacement therapy and risk of venous thromboembolism in postmenopausal women: systematic review and meta-analysis

Marianne Canonico et al. · BMJ · 2008

DOI 10.1136/bmj.39555.441944.be

Meta-analysis · 17 studiesCited 558×
Read the paper
DOI resolved against Crossref · corpus check 2026-06-10

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