The Women's Health Initiative (WHI) is a major 15-year research program to address the most common causes of death, disability and poor quality of life in postmenopausal women -- cardiovascular disease, cancer, and osteoporosis.

Findings from the WHI Postmenopausal Hormone Therapy Trials

The WHI was launched in 1991 and consists of a set of clinical trials and an observational study, which together involve more than 161,000 generally healthy postmenopausal women.

The clinical trials were designed to test the effects of postmenopausal hormone therapy, diet modification, and calcium and vitamin D supplements on heart disease, fractures, and breast and colorectal cancer.

The hormone trial had two studies: the estrogen-plus-progestin study of women with a uterus and the estrogen-alone study of women without a uterus. (Women with a uterus were given progestin in combination with estrogen, a practice known to prevent endometrial cancer.) In both hormone therapy studies, women were randomly assigned to either the hormone medication being studied or to placebo. Those studies have now ended. The women in these studies are now participating in a follow-up phase, which should last until 2007.

• Questions and Answers About the WHI Postmenopausal Hormone Therapy Trials
  
  
• The Estrogen-Alone Study
  
  
• The Estrogen-Plus-Progestin Study