Painkillers such as aspirin and ibuprofen can reduce the risk of breast cancer by up to 21%, a study has shown.
Research from the University of British Columbia in Canada found that using the common medicines lowered the risk of breast cancer by 12% compared with taking nothing.
An analysis concentrating solely on aspirin showed a 13% reduction of risk, while ibuprofen on its own reduced the chances of developing breast cancer by 21%.
Both belong to a class of medicines known as Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), which work by inhibiting two enzymes in the body linked to the immune system.
Cox 1 and 2 enzymes help to drive inflammation, and are thought to play several roles in the promotion of cancer.
They are believed to affect processes such as cell proliferation and death, the generation of blood vessels that feed tumours, tissue invasion by cancer cells, and immune responsiveness.
Dr Sarah Rawlings, head of policy at Breakthrough Breast Cancer, said: "Anti-inflammatory drugs can have potentially serious side-effects when taken over a long period. Until the long-term effects of taking these drugs for breast cancer prevention are known, we would urge women worried about their risk of breast cancer to talk to their GP."