The findings, published in the journal Gut, boost evidence that the digestive tract's complex network of bacteria may play a key role in cancer emergence.
Earlier research has linked antibiotic use to developing bowel cancer but the potential association with these abnormal growths had not been explored.
To find out more, Andrew Chan of the Massachusetts General Hospital in Boston combed through health records for 16,642 women who were 60 or older in 2004.
The women were enrolled in the Nurses Health Study, which has been following the health of 121,700 nurses in the United States since 1976. The nurses' medications are included in the monitoring.
The women examined in the new study had had at least one colonoscopy between 2004 and 2010. During that period, 1,195 cases of polyps were diagnosed.
The researchers found an increased risk of polyps among women who had taken antibiotics for a total of two months or more over a two-decade span.
Women who did so in their 20s and 30s had a 36-percent greater chance of polyps forming compared to counterparts who did not extensively use antibiotics.
The risk jumped by 70 percent in women who took antibiotics for at least two months while they were in their 40s and 50s.
"Long-term antibiotic use in early-to-middle adulthood was associated with increased risk of colorectal adenoma," the study said, using the technical term for polyps.
The study was not based on a controlled experiment, so the evidence that antibiotics somehow lead to the appearance of polyps remains circumstantial, the researchers noted.
But there is a plausible explanation for how this might happen, they added.
