Double the hormone, double the risk. Or so says one study of older women who take hormone pills. When estrogen and testosterone are combined, women face twice the chance of getting breast cancer, according to a study of more than 70,000 nurses. This type of combination therapy may help with mood, libido, and bone density — but the possible risk of breast cancer may just outweigh these benefits. These findings, published in Monday’s Archives of Internal Medicine, add to the evidence that certain types of hormone supplements — like estrogen-progestin pills — increase risk of breast cancer, strokes, and heart attacks in women. Other research points to a link between breast cancer and high natural levels of testosterone.

Women’s natural levels of estrogen and testosterone decrease with menopause. Use of supplements has climbed over the past 24 years, perhaps putting more women at more risk. Estrogen-testosterone pills are sold under the brand names Estratest and Estratest H.S. and appear on a Washington-based advocacy group’s “Worst Pills” list because of breast cancer risk.