Antibiotics can save lives, but a recent study suggests that there may be some negative side effects, too. According to a press release from the Johns Hopkins University Bloomberg School of Public Health, researchers found that kids who take antibiotics gained weight faster than kids who didn’t.

The study was published in the International Journal of Obesity, and suggests that antibiotics can have a negative effect on body mass index throughout childhood, making kids more susceptible to weight gain.

According to lead researcher Brian S. Schwartz, a professor at the Department of Environmental Health Sciences at the Bloomberg School, “Your BMI may be forever altered by the antibiotics you take as a child. Our data suggest that every time we give an antibiotic to kids they gain weight faster over time.”

The researchers looked over medical records for 163,820 children between the ages of three and 18, and compared their BMI with their antibiotic use throughout the course of their childhoods.

They found that by age 15, kids who had received seven courses of antibiotics over the course of their childhood weighed an average of three pounds more than children who didn’t. Roughly 21 percent of the children in the sample had received antibiotics more than seven times.

According to Schwartz, “While the magnitude of the weight increase attributable to antibiotics may be modest by the end of childhood, our finding that the effects are cumulative raises the possibility that these effects continue and are compounded into adulthood.”