Flomax, a drug commonly used to treat benign prostate enlargement, is effective in breaking up large kidney stones, a new study finds.

Kidney stones, which are “pebbles” of salt and minerals in the kidney, occur in one out of  11 people in the U.S.

Small stones can often pass through the urinary tract, but larger stones can become stuck, causing severe pain, a problem that results in a million emergency room visits a year, statistics show.

Previously, Flomax (tamsulosin) had been used to treat small kidney stones because it relaxes the smooth muscle of the bladder wall, which enables them to more easily pass. The new study showed, however, that the drug is actually more effective on large kidney stones.

The researchers found that 83 percent of patients using Flomax were able to pass large stones, compared to 61 percent with a placebo.

Scientists believe the drug acts on the stones to break them into smaller pieces, making them more likely to pass.