What are the risks and adverse effects of hormone replacement therapy in menopausal women (age ≥ 45)?

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Last updated: September 14, 2026 • View editorial policy

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Hormone Replacement Therapy Causes Both Significant Harms and Benefits

Hormone replacement therapy (HRT) causes increased risks of coronary heart disease events, stroke, pulmonary embolism, invasive breast cancer, and venous thromboembolism, while simultaneously reducing risks of colorectal cancer and hip fractures. 1, 2, 1

Quantified Absolute Risks (Per 10,000 Women Per Year)

Based on the Women's Health Initiative study of estrogen-progestin therapy in women ages 50-79 years, HRT causes:

Increased Risks:

  • 7 additional CHD events
  • 8 additional strokes
  • 8 additional pulmonary emboli
  • 8 additional invasive breast cancers

Decreased Risks:

  • 6 fewer colorectal cancers
  • 5 fewer hip fractures 1, 2, 1

Timing-Dependent Risk Profile

Early Risks (First 1-2 Years)

  • Venous thromboembolism risk peaks immediately, with 3.5-fold increased risk in the first year 1
  • CHD and stroke risks evident shortly after initiation 1

Long-Term Risks (With Continued Use)

  • Breast cancer risk increases with duration of therapy 1

Specific Harms by Hormone Type

Combined Estrogen-Progestin Therapy

  • Endometrial cancer: No increased risk (protective effect observed) 1
  • Breast cancer: Increased risk with long-term use 1
  • Cardiovascular disease: Increased CHD incidence (HR 1.29), contrary to earlier observational data suggesting protection 1
  • Stroke: Increased thromboembolic stroke (RR 1.20) 1
  • VTE: 2-fold increased risk (RR 2.14) 1

Unopposed Estrogen (Post-Hysterectomy)

  • Endometrial cancer: Dramatically increased risk (RR 2.3), rising to RR 9.5 with 10 years of use 1
  • Bone health: Increased bone mineral density, reduced fracture risk 1
  • Colorectal cancer: Reduced risk 1
  • VTE, cholecystitis, stroke: Increased risks 1

Critical Clinical Pitfalls

The cardiovascular "protection" seen in observational studies was due to selection bias—healthier, higher socioeconomic status women were more likely to use HRT. When controlled for socioeconomic factors, no cardiovascular benefit exists (RR 0.97) 1. This represents one of the most important reversals in modern medicine.

Age-Specific Considerations

Women initiating HRT after age 65 face substantially elevated risks without clear benefits for chronic disease prevention. The benefit-risk ratio becomes unfavorable due to greater absolute risks of CHD, stroke, VTE, and dementia in this age group 1.

Formulation-Specific Risks

The evidence base derives primarily from conjugated equine estrogen (CEE) with medroxyprogesterone acetate (MPA). Other formulations, routes, and doses lack sufficient data to determine if they offer more favorable risk profiles 1.

Transdermal estrogens appear to have lower VTE, stroke, and MI risk compared to oral preparations 3, though this comes from more limited evidence.

Insufficient Evidence Areas

Evidence remains insufficient to determine HRT's effects on:

  • Dementia and cognitive function
  • Ovarian cancer risk
  • Breast cancer mortality
  • Cardiovascular disease mortality
  • All-cause mortality 1

The Bottom Line for Clinical Practice

HRT should not be used for chronic disease prevention in any age group 1, 2, 1. The harms outweigh benefits for this indication in most women.

For symptomatic relief of vasomotor or urogenital symptoms, use requires:

  • Lowest effective dose
  • Shortest duration necessary
  • Counseling about early VTE/CHD/stroke risks (1-2 years)
  • Counseling about increasing breast cancer risk with longer duration
  • Shared decision-making incorporating individual risk factors 1

Women who have not had a hysterectomy must receive progestin with estrogen to prevent endometrial cancer 1.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.