The Women’s Health Initiative (WHI) was a clinical trial with more than 10,000 women that had to be halted before its scheduled end because the interim health effects seen on women were particularly harmful.  Women who participated and received combined estrogen plus progestin experienced increases overall risks of breast cancer, stroke, coronary heart disease, venous thrombeoembolism (VTE).  This study was glaring warning sign that the use of combination estrogen and progestin was harmful to women and that indeed, more research on menopause in women had to be conducted.
 
Although the WHI originally sought to determine if hormone therapy reduced the risk of heart disease in women, in fact, the exact opposite was seen. In fact, Dr. Manson and her research team determine that hormone therapy did not protect women from cardiac events and instead “may increase the risk of CHD.  This treatment should not be prescribed for the prevention of cardiovascular disease.”
 
After the study came to an abrupt halt, researcher attempted to gain a deeper understanding of the results by looking at the impact from both short-term and long-term hormone therapy.  Some  researchers have explored the possible detection bias in these subsequent studies because the WHI results gained such widespread publicity and might have contributed to an overestimation of the risks of cardiovascular outcomes from the hormone therapy.  

Resource Link:
Shapiro, S. 2006.  “Risk of Cardiovascular Disease in Relation to the Use of Combined Postmenopausal Hormone Therapy: Detection Bias and Resolution of Discrepant Findings in Two Women’s Health Initiative Studies,” Climacteric, 9: 416-420.
 
Grady, Deborah et al, 2002.  “Cardiovascular Disease Outcomes During 6.8 Years of Hormone Therapy: Heart and Estrogen/Progestin Replacement Study Follow-Up (HERS II),”  JAMA. 2002;288:49-57.
 
 
Related Links:
Manson, JE et al, 2003.  “Estrogen plus progestin and the risk of coronary heart disease”  New England Journal of Medicine 349; 523-34.
 
US Food and Drug Administration, Center for Drug Evaluation and Research. FDA statement on the results of the Women’s Health Initiative (8/13/2002). Rockville, MD: US Food and Drug Administration, 2002. Available at: http://www.fda.gov/CDER/DRUG/safety/WHI_....