Narrator: For over a decade, many post-menopausal women have considered hormone replacement therapy the best way to combat some of the more dangerous effects of growing old. But a new report indicates that estrogen replacement may not be effective in preventing problems like heart disease, Alzheimer's and fractures. Dr. Deborah Grady of the University of California, San Francisco, says there are many reasons why estrogen therapy should not be prescribed for prevention.

Grady: One, and most importantly, you're taking a totally healthy person who feels well. Do you have any chance of making her feel better? No, not much. But you can make them feel worse and you can cause them to develop adverse effects and side effects.

Narrator: Grady adds that prescribing estrogen widely is ineffective - and risky.

Grady: Everybody's at risk and only a few of them are going to benefit. And for this reason I really think that the benefits should be proven in the best form of research, which is the randomized trial.

Narrator: For Science Today, I'm Larissa Branin.