Bile is a liquid containing cholesterol, bilirubin, bile salts and other substances. Gallstones, rock-like material within the gallbladder, form when there is too much cholesterol or bilirubin in the bile or if the gallbladder does not contract normally to expel the bile. Risk factors for gallstones include obesity, a high-fat diet, ethnicity, female gender, pregnancy, older age, diabetes, rapid weight loss and a family history of gallstones. An increased risk of gallstones is also seen when taking some medications.
Estrogen increases the amount of cholesterol in the bile as well as decreases gallbladder motility, both of which lead to increased gallstone formation. Administration of any estrogen-containing compound such as birth control pills or hormone replacement therapy for menopause increases the risk of gallstone formation because these compounds lead to excess estrogen and excess bile cholesterol. Hormone replacement therapy using patches, rather than pills, does not carry the same increased risk of gallstone formation.
Some types of cholesterol-lowering drugs, gemfibrozil and fenofibrate, lower the amount of cholesterol in the bloodstream but increase the cholesterol in bile, leading to increased risk of gallbladder stone formation. Statins, the most popular kind of drugs used for lowering cholesterol, do not have this side effect.
Octreotide is a drug used to treat acromegaly and certain kinds of tumors. This drug decreases gallbladder motility, which, according to Drugs.com, leads to gallstone formation in about 29 percent of people taking octreotide; another 20 percent develop gallbladder sludge. The risk of gallstone formation decreases after withdrawal of the drug.
Total Parenteral Nutrition
Total parenteral nutrition, or TPN, is a pharmacologic mixture of glucose, fatty acids, amino acids and several other vitamins and minerals given intravenously 24 hours a day to people who cannot get enough nutrition by mouth alone. The high caloric content of TPN leads to decreased gallbladder motility and gallbladder sludge, significantly increasing the risk of gallstone formation. Stopping the glucose infusion a few hours every day or the addition of certain medications helps decrease gallstone formation in TPN patients.