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Experts say healthy women who are at an increased risk for breast cancer because of family or personal history should take drugs to lower their risk.

The drugs tamoxifen and raloxifene can lower the risk of breast cancer and may be worth taking even though the drugs can have adverse effects such as blood clots and strokes, experts said.

The panel from the United States Preventive Services Task Force recommended that healthy woman between the ages of 40 to 70 are assessed for their odds of breast cancer. The drugs should be prescribed to those patients whose risk is above average, but only if their chances of developing blood clots and strokes are low.

The adverse effects caused the panel to advise that the drugs not be prescribed for women unless they are at increased risk of breast cancer.

"There is evidence of benefit for certain women," said Dr. Wanda K. Nicholson, a task force member and an associate professor of obstetrics and gynecology at the University of North Carolina, School of Medicine in Chapel Hill.

Dr. Nicholson has recommended tamoxifen and raloxifene for some of her own higher-risk patients. She said some take them and some choose not to.

"The take-home point for women is to have that initial conversation with their provider," she said.

The task force recommendations, which were based on research analysis, are being published in draft form and are open for public comment until May 13. The recommendations are largely based on new data that helped confirm and clarify the risks of the drugs, but the task force advice dates back to an earlier report in 2002.

Tamoxifen and raloxifene block the effects of estrogen and can lower the risk of a type of breast cancer that is stimulated by the hormone. Approximately 75 percent of breast cancers fall into this category. For women who have already had breast cancer, Tamoxifen is commonly used to prevent recurrences and can reduce the risk of fractures. Raloxifene is also prescribed to prevent fractures in women with osteoporosis.

While doctors view these drugs as a rare opportunity to reduce the risk of cancer, some women simply think taking the drugs is trading one risk for another. Many healthy women who are at an increased risk for the disease do not agree with taking the pills when they may have dangerous or unpleasant side effects.

Tamoxifen and raloxifene not only increase the risk of blood clots and stroke, but can also cause hot flashes and vaginal irritation, like dryness and pain, that can interfere with a woman's sex life. The drugs can also lead to cataracts and uterine cancer.

In the United States, 232,000 new cases of breast cancer are expected to occur this year, and approximately 40,000 lives will be claimed by the disease.

Experts estimated that over the next five years 23.5 cases of invasive breast cancer would occur per 1,000 women with an increased risk of breast cancer. If the women took one of the drugs, 7 to 9 cases would be prevented over five years.

But over the five year period, 4 to 7 women per 1,000 taking the drugs would develop blood clots, and there would be 4 extra cases of uterine cancer per 1,000 women taking tamoxifen, which approximately doubles both of those risks.

According to the task force, a woman is likely to benefit from the drugs if her odds of developing breast cancer in the next five years are 3 percent or higher. One method of estimating the risk uses and online tool asking a series of questions about the patient's family history and health, comparing it to the average for women the same age.

At age 40 the average woman has a 0.6 percent risk of developing breast cancer over the next five years; at age 50, 1.3 percent; at age 60, 1.8 percent; at age 70, 2.2 percent. Plugging risk factors into the calculator, like mothers or sisters with breast cancer, or a personal history of breast biopsies, makes the risk go up, according to the New York Times.

While these estimates may be useful in predicting the risk for large populations, experts warn they do not work very well for individuals.

"Most women identified as 'high risk' will not develop breast cancer, and the majority of breast cancer cases will arise in women who are not identified as having increased risk," warned the task force in a statement. The group also noted that the type of risk calculator generally used is not recommended for women with mutations in BRCA genes, which greatly increase the risk of breast cancer.

Several large controlled studies were analyzed by Dr. Heidi Nelson, a research professor at Oregon Health and Science University in Portland, Oregon, and her team. The researchers found the drugs could reduce the incidence of invasive cancer by 30 percent to 68 percent, compared with placebos. The analysis also found that tamoxifen had a greater protective effect than raloxifene, but it was more likely to cause blood clots. Women over 50 were more likely to develop blood clots from the drugs, or uterine cancer while taking tamoxifen.

Some studies found women would be more willing to take the drugs if they could prevent breast cancer entirely, rather than just lowering the risk, or if the drugs had no side effects, Dr. Nelson noted.

It is important for doctors and patients to keep in mind that the adverse effects were more common in older women, Dr. Nelson said. Younger women who had a condition called atypical hyperplasia, did seem to be at added risk and might be among the best candidates for taking the drugs, she added. The data suggested that a five-year course of treatment could have protective effects that would continue even when the drugs were stopped.