(Ivanhoe Newswire) -- New research shows tamoxifen use is down among women who need it most, and researchers can't pinpoint exactly why.

The drug tamoxifen is prescribed for reducing the risk of breast cancer in women who are at high risk. Researchers at the National Cancer Institute looked at data from National Health Interview Surveys between 2000 and 2005, which included more than 10,000 women each year. In 2000, 20 percent of the survey population was taking tamoxifen; In 2005, that number was 8 percent.

Researchers believe the decreased use of tamoxifen can be attributed to reasons including side effects, lack of physician awareness of availability, prescription reluctance, lack of education and skepticism about benefits and risks.

“The decision to use a drug like tamoxifen in women at high risk for but who do not yet have a diagnosis of breast cancer is not easy," lead study author Erika A. Waters, Ph.D., M.P.H, was quoted as saying. "It is dependent upon the woman's personal choice, which can be influenced by many factors, not just her medical eligibility."

SOURCE: Cancer Epidemiology, Biomakers &Prevention February 2010