London: Women who undergo hormone replacement therapy (HRT) for menopause are much more likely to develop painful kidney stones.
Researchers from the University of Texas, US, studied 24,000 post-menopausal women over five years. They found that those who took hormones had a 21 percent higher risk of getting kidney stones compared to those who took a dummy pill.
The risks were similar for women taking Prempro, pills containing estrogen plus progestin - or Premarin, estrogen-only pills, the Daily Mail reported.
Recent data suggests that about six percent of postmenopausal women develop kidney stones, according to the journal Archives of Internal Medicine.
The kidneys remove waste products from the blood and transfer them into the ureter. Occasionally, this waste can form into crystals that collect together into stone-like lumps.
They can grow to the size of golf balls and cause severe pain. If the stones block the urinary system, they can cause infection and kidney damage.
Large stones are sometimes treated with non-invasive shock wave therapy or surgery.
Study leader Naim Maalouf said women considering HRT to ease hot flushes and other symptoms such as mood swings should "look at the bigger picture", weighing those benefits against the risks for kidney stones.
He added that HRT has also been linked with far more serious health problems such as breast cancer and heart attacks.