Prescriptions for hormone replacement therapy (HRT) are very common for post-menopausal women. The purpose of HRT is to moderate the symptoms of menopause, and ideally to avoid some of the health consequences associated with reduced hormone levels, such as osteoporosis. Tens of millions of women receive prescriptions for medications such as Prempro and Premarin, and hormone replacement therapy generates revenues in the billions of dollars for drug companies.
The Women's Health Initiative (WHI), sponsored by the National Heart, Lung, and Blood Institute (NHLBI) and units of the National Institutes of Health, commenced in 1991, with a focus on finding ways to prevent heart disease, breast cancer, colorectal cancer, and osteoporosis. The study included 161,000 healthy post-menopausal women.
One of the WHI's clinical studies involved 16,608 post-menopausal women with a uterus who took either estrogen plus progestin, in the form of the medication Prempro, manufactured by Wyeth, or a placebo. In July, 2002, after only 5.2 years, this clinical study was terminated when the NHLBI concluded that the risks of the therapy outweighed its benefits.
- The study suggested a significant increase in the incidence of abnormal mammograms, and incidence and severity of breast cancer, in the group of women who were taking Prempro, as compared to the placebo group.
- There was also concern of increased risk of heart attack, stroke, or pulmonary embolism (blood clots in the lungs).
Although Premarin contains only estrogens, as compared to the combination of estrogen and progestin in Prempro, some law firms assert that its use in hormone replacement therapy has similar side effects to those found in Prempro users, and thus that it carries similar risks to patients.
Wyeth Pharmaceuticals, the manufacturer of Prempro, took the position that its warning labels are adequate and that, if properly used in appropriate cases, hormone replacement therapy with Prempro is both safe and effective. Wyeth was acquired by Pfizer in 2009.
A number of law firms recruited potential clients to litigate over injuries allegedly caused by Prempro, followed by class action litigation. The lawsuits alleged that even though Prempro can offer some legitimate medical benefits, the risks associated with its use render it inherently unsafe. There was significant difference of opinion as to whether there was sufficient evidence of causation - that is, whether Prempro was the actual cause of the medical conditions found in the study, or similar medical conditions in any given patient - that many lawyers questioned whether litigation over hormone replacement therapy was viable.
By 2012, Pfizer has paid approximately $896 million to resolve close to sixty percent of the cases alleging that its menopause drugs caused cancer in women.