Evidence question

PubMed sourcedAbstract-based analysisUpdated Sep 2026Human reviewedUpdated Aug 2026

Evidence / Menopause & Women's Health

CoverageMenopause & Women's Health

Does hormone replacement therapy increase venous thromboembolism risk?

Reviewed by Neal Rouzier, MD, Preventive Medicine · Aug 2026

Updated Aug 2026·14 studies analyzed·3 core studies·Applies to: perimenopausal and early postmenopausal women

Bottom line

Oral estrogen increases venous thromboembolism risk compared with no therapy. Transdermal estrogen appears to carry lower thrombotic risk in observational studies and is often preferred in women at elevated VTE risk.[1–6]

Evidence confidence

Evidence Confidence

High
LimitedModerateHigh

Multiple high-quality studies directly address this question, with generally consistent findings.

Key uncertainty. Absolute VTE risk varies by age, obesity, thrombophilia, route, and progestogen type; transdermal observational data have residual confounding.

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Also asked

Does HRT cause blood clots?▼

Oral estrogen-based HRT is associated with increased venous thromboembolism risk. Transdermal estrogen avoids first-pass hepatic metabolism and does not appear to increase VTE risk in observational data.

Transdermal vs oral estrogen clot risk▼

Observational studies consistently show transdermal estradiol does not increase VTE risk, while oral estrogen does. For women with elevated baseline VTE risk, transdermal is the preferred route.

Who should not take HRT because of blood clot risk?▼

Women with a personal or strong family history of VTE, thrombophilia, or active thrombotic disease should generally avoid oral HRT. Transdermal estrogen may be considered on a case-by-case basis with specialist input.

Micronized progesterone VTE risk vs synthetic progestins▼

Some observational data suggest micronized progesterone carries lower VTE risk than certain synthetic progestins. Evidence is not from randomized trials; route of estrogen delivery remains the stronger determinant.

HRT blood clots▼

Oral estrogen increases venous thromboembolism risk compared with no therapy. Transdermal estrogen appears to carry lower thrombotic risk in observational studies and is often preferred in women at elevated VTE risk.

Oral estrogen VTE▼

Oral estrogen increases venous thromboembolism risk compared with no therapy. Transdermal estrogen appears to carry lower thrombotic risk in observational studies and is often preferred in women at elevated VTE risk.

Body of evidence

Clinical Evidence Brief

RAGMD analyzed 12 relevant studies.

Overall finding

5 studies address venous thromboembolism, with weighted findings showing mixed findings. 5 studies address breast cancer, with weighted findings showing mixed findings. 4 studies address mortality, with weighted findings showing mixed findings. 4 studies address vasomotor symptom associations, with weighted findings showing mixed findings. 5 randomized or systematic-review reports and 5 observational studies address treatment. Prefer transdermal estrogen in women with elevated thrombotic risk, obesity, or prior VTE when systemic estrogen is indicated.

Evidence by outcome

Direction: ↑ Favors treatment / reassuring · ↓ Harm signal · ↔ No clear effect · ± Mixed · ↗ Observational link · ? Unclear

Mixed

Venous thromboembolism

moderate · 5 studies

5 studies address venous thromboembolism, with weighted findings showing mixed findings. This is an objectively measured outcome. This is a hard clinical endpoint.

Objectively measured · Hard clinical endpoint

Studies

PMID 30626577PMID 35713694PMID 12117397PMID 26544651PMID 36749328
Mixed

Breast cancer

moderate · 5 studies

5 studies address breast cancer, with weighted findings showing mixed findings. This is an objectively measured outcome. This is a hard clinical endpoint.

Objectively measured · Hard clinical endpoint

Studies

PMID 35713694PMID 12117397PMID 32721007PMID 23543779PMID 36749328
Mixed

Mortality

moderate · 4 studies

4 studies address mortality, with weighted findings showing mixed findings. This is an objectively measured outcome. This is a hard clinical endpoint.

Objectively measured · Hard clinical endpoint

Studies

PMID 30626577PMID 12117397PMID 32721007PMID 23543779
Mixed

Vasomotor symptom associations

moderate · 4 studies

4 studies address vasomotor symptom associations, with weighted findings showing mixed findings. This is a patient-reported / subjective outcome.

Patient-reported

Studies

PMID 29322164PMID 26838086PMID 36749328PMID 34513605
Unclear

Bone mineral density

moderate · 1 study

1 study addresses bone mineral density, with weighted findings showing unclear findings. This is an objectively measured outcome. This is a surrogate endpoint and does not by itself prove a hard clinical outcome.

Objectively measured · Surrogate endpoint

Studies

PMID 35713694
Harm signal

Fractures

moderate · 1 study

1 study addresses fractures, with weighted findings showing harm. This is an objectively measured outcome. This is a hard clinical endpoint.

Objectively measured · Hard clinical endpoint

Studies

PMID 12117397

Magnitude / clinical importance

Validated effect estimates in the analyzed set include odds ratio 1.58; HR = 1.55. Statistical significance is not the same as clinical importance.

Where quantified, effects were often statistically detectable but small in absolute terms.

Agreement across studies

Most studies agree on vasomotor symptom associations (mixed findings), while venous thromboembolism findings are mixed findings and less consistent across domains.

Supports main conclusion: 5 · Neutral / mixed: 7 · Credible conflicting: 0

Study counts describe the landscape; RAGMD weights studies according to design, quality, and directness.

Conflicting findings

  • Available evidence comparing the transdermal and oral administration routes for HRT is limited and of low quality, recommending further investigations.
  • Overall health risks exceeded benefits from use of combined estrogen plus progestin for an average 5.2-year follow-up among healthy postmenopausal US women.
  • The influence of menopausal hormone therapy on breast cancer remains unsettled with discordant findings from observational studies and randomized clinical trials.
  • MHT has a complex pattern.

Risks & harms

5 studies report safety-relevant findings. Design mix: Randomized controlled trial, Systematic review / meta-analysis, Study design not clearly classified, Narrative review. Rare-event inference should not rest on underpowered trials alone.

Who this applies to

Most studies included perimenopausal and early postmenopausal women.

What remains uncertain

  • Absolute VTE risk varies by age, obesity, thrombophilia, route, and progestogen type; transdermal observational data have residual confounding.
  • Absolute VTE risk varies by age, obesity, thrombophilia, route, and progestogen type; transdermal observational data have residual confounding.
  • Surrogate improvement does not prove a hard clinical outcome.
  • Typical subjective cognitive complaints are not established as equivalent to dementia.

Clinical takeaway

Prefer transdermal estrogen in women with elevated thrombotic risk, obesity, or prior VTE when systemic estrogen is indicated. Oral estrogen carries higher VTE signal in observational data; progestogen type and route also influence thrombotic risk.

Mixed

Venous thromboembolism?

Mixed findings

moderate[30626577 · 35713694 · 12117397 · 26544651 · 36749328]

Mixed

Breast cancer?

Mixed findings

moderate[35713694 · 12117397 · 32721007 · 23543779 · 36749328]

Mixed

Mortality?

Mixed findings

moderate[30626577 · 12117397 · 32721007 · 23543779]

Mixed

Vasomotor symptom associations?

Mixed findings

moderate[29322164 · 26838086 · 36749328 · 34513605]

Unclear

Bone mineral density?

Unclear findings

moderate[35713694]

Harm signal

Fractures?

Harm

moderate[12117397]

Mixed

Mood-related cognitive symptoms?

Mixed findings

moderate[29322164]

Reassuring

Hormone therapy effects on cognition?

Benefit

limited[37755656 · 35017407]

5 randomized or systematic-review reports and 5 observational studies address treatment. Weighted treatment findings show mixed findings.

5 RCT / systematic review · 5 observational

Large randomized trials strongly influence the conclusion

3 landmark studies with randomized or systematic-review designs strongly inform this conclusion.

Supporting studies provide additional context

11 supporting studies add context beyond the core evidence base.

Regimen & duration

Observational and supporting studies provide context and do not outrank higher-appropriateness designs.

Long-term uncertainty

Evidence beyond long follow-up windows and in certain subgroups remains less complete.

12 analyzed studies

Strongest evidence

Archives of gynecology and obstetrics2023

Landmark studyPMID 35713694

Effects of transdermal versus oral hormone replacement therapy in postmenopause: a systematic review.

Available evidence comparing the transdermal and oral administration routes for HRT is limited and of low quality, recommending further investigations. VTE risk can be considered the clearest and strongest clinical difference between the two administration routes, supporting the transdermal HRT as safer than the oral…

Systematic review
Evidence
Relevance

Supporting literature

Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial.

Efficacy of Transdermal Estradiol and Micronized Progesterone in the Prevention of Depressive Symptoms in the Menopause Transition: A Randomized Clinical Trial.

Association of Menopausal Hormone Therapy With Breast Cancer Incidence and Mortality During Long-term Follow-up of the Women's Health Initiative Randomized Clinical Trials.

+8 more

More in this focus area

Related evidence analyses

Other structured clinical questions in Menopause & Women's Health.

Does hormone replacement therapy increase breast cancer risk?

Combined estrogen-progestin therapy is associated with a small increased breast cancer risk in WHI and observational data. Estrogen-alone in hysterectomized women showed lower risk in WHI, but interpretation depends on regimen, duration, and individual risk factors.

10 linked studies

Does hormone replacement therapy reduce cardiovascular risk in early menopause?

The timing hypothesis suggests earlier initiation may differ from late initiation, where WHI showed harm for combined therapy. Current guidelines emphasize individualized risk assessment rather than routine cardioprotection.

14 linked studies

Is there a critical timing window for cardiovascular benefit from HRT?

The critical-window concept proposes that starting HRT closer to menopause may yield different cardiovascular effects than starting later. WHI subgroup analyses inform but do not prove this hypothesis for routine practice.

14 linked studies

Is progestogen required to protect the endometrium with estrogen therapy?

Systemic estrogen in women with a uterus requires adequate progestogen exposure to prevent endometrial hyperplasia. Micronized progesterone and progestins differ in metabolic and VTE profiles.

14 linked studies

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