Figure 1:

Risk of gallbladder disease (as defined by occurrence of cholecystectomy) associated with six months of continuous use of oral contraceptives containing different progestins. Women using levonorgestrel served as the reference group. Rate ratios were adjusted for age, calendar time, sickle-cell anemia, diabetes mellitus, inflammatory bowel disease, obesity, pancreatitis, smoking, and use of statins and fibrates. A rate ratio greater than 1.0 indicates an increased risk of gallbladder disease. CI = confidence interval, ref = reference group.