These results were later supported in trials from the United Kingdom, but not in more recent studies from France and China. Genetic polymorphism appears to be associated with inter-individual variability in metabolic response to HRT in postmenopausal women. The WHI reported statistically significant increases in rates of breast cancer, coronary heart disease, strokes and pulmonary emboli. The study also found statistically significant decreases in rates of hip fracture and colorectal cancer. "A year after the study was stopped in 2002, an article was published indicating that estrogen plus progestin also increases the risks of dementia." The conclusion of the study was that the HRT combination presented risks that outweighed its measured benefits. The results were almost universally reported as risks and problems associated with HRT in general, rather than with Prempro, the specific proprietary combination of CEEs and MPA studied. After the increased clotting found in the first WHI results was reported in 2002, the number of Prempro prescriptions filled reduced by almost half. Following the WHI results, a large percentage of HRT users opted out of them, which was quickly followed by a sharp drop in breast cancer rates. The decrease in breast cancer rates has continued in subsequent years. An unknown number of women started taking alternatives to Prempro, such as compounded bioidentical hormones, though researchers have asserted that compounded hormones are not significantly different from conventional hormone therapy.The other portion of the parallel studies featured women who were post hysterectomy and so received either placebo progestogen or CEEs alone.
Skin and vaginal routes of hormone therapy are not subject to first pass metabolism, and so lack the anabolic effects that oral therapy has on liver synthesis of vitamin K-dependent clotting factors, possibly explaining why oral therapy may increase blood clot formation.While a 2018 review found that taking progesterone and estrogen together can decrease this risk, other reviews reported an increased risk of blood clots and pulmonary embolism when estrogen and progestogen were combined, particularly when treatment was started 10 years or more after menopause and when the women were older than 60 years.The risk of venous thromboembolism may be reduced with bioidentical preparations, though research on this is only preliminary. Stroke
Multiple studies suggest that the possibility of HRT related stroke is absent if therapy is started within five years of menopause, and that the association is absent or even preventive when given by non-oral routes. Ischemic stroke risk was increased during the time of intervention in the WHI, with no significant effect after the cessation of therapy and no difference in mortality at long term follow up. When oral synthetic estrogen or combined estrogen-progestogen treatment is delayed until five years from menopause, cohort studies in Swedish women have suggested an association with hemorrhagic and ischemic stroke. Another large cohort of Danish women suggested that the specific route of administration was important, finding that although oral estrogen increased risk of stroke, absorption through the skin had no impact, and vaginal estrogen actually had a decreased risk.