Research

Hormonal

Current use of oral estrogen increases the risk of venous thromboembolism in postmenopausal women, with the highest risk occurring during the first year of treatment.

If you are a postmenopausal woman considering hormone replacement therapy, be aware that taking estrogen orally increases your risk of blood clots (venous thromboembolism), especially during the first year of use. This risk is roughly 2.5 times higher than in non-users. However, using estrogen through the skin (transdermal patches/gels) does not appear to increase this clotting risk, making it a potentially safer option to discuss with your doctor.

StrongSupportsHIGH confidence
Meta-analysis of observational studies showed that oral oestrogen but not transdermal oestrogen increased the risk of venous thromboembolism... The risk of venous thromboembolism in women using oral oestrogen was higher in the first year of treatment (4.0, 2.9 to 5.7) compared with treatment for more than one year (2.1, 1.3 to 3.8; P<0.05).
Marianne Canonico et al. · BMJ · 2008

Why this rating

Based on a systematic review and meta-analysis of 8 observational studies and 9 randomized controlled trials.

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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