Cancer charities are calling it a game changer, offering women with a family history of breast cancer a course of pills on the NHS in England and Wales.
It isn't as effective at preventing the disease as a masectomy, but it is cheaper and less traumatic. Taking the pills for five years can give 15 or more years of protection.
ITV News' Laurence McGinty reports:
The drug tamoxifen is already being used as a treatment for breast cancer - but this is the first time it will be offered as a preventative measure in the United Kingdom.
Gareth Evans, Professor of Medical Genetics at St Mary's Hospital, Manchester told the Associated Press that the advantage of the taking tamoxifen was that the effects after women had stopped taking it.
"The effects of the treatment last 15 to 20 years into the future so it's not just preventing breast cancer when you take it but it's preventing it for many, many years afterwards," he said.
The treatment will be offered to women aged 35 and over considered to be at a high risk (above 30 percent) or moderate risk (17 to 30 percent) of developing breast cancer.
Tamoxifen has been used as a preventative medicine for high-risk breast cancer patients in the United States since 2002.