Breast cancer experts reacted with caution and surprise, citing scant and conflicting research. Tamoxifen is known to cut the risk of breast cancer recurrence, but only one study in the United States has suggested it could prevent the disease in healthy women, while two other recent studies from Europe suggested it did not. He added that he would not prescribe it, based on data available now. We really don't have a complete picture of risks and benefits over the long term.
Tamoxifen has major side effects.
Tamoxifen also cannot be taken by women trying to get pregnant. The FDA is expected to decide the issue by the end of this year, but it usually follows the advisory panel's recommendation. Even those who believe the drug is promising for treatment of breast cancer have strong reservations about its widespread use in healthy women. It's a very important personal decision. It is not for average-risk women.