Bile acid sequestrants such as cholestyramine (Questran, Prevalite), colestipol (Colestid, Flavored Colestid ), and colesevelam (Welchol) are medications for lowering LDL cholesterol in conjunction with diet modification.

Bile acid sequestrants bind bile acids in the intestine and increase the excretion of bile acids in the stool. This reduces the amount of bile acids returning to the liver and forces the liver to produce more bile acids to replace the bile acids lost in the stool. In order to produce more bile acids, the liver converts more cholesterol into bile acids, which lowers the level of cholesterol in the blood.

Bile acid sequestrants have modest LDL cholesterol lowering effects. Low doses (for example 8 gram/day of Cholestyramine) can lower LDL cholesterol by 10%-15%. But even high doses (24 gram/day of cholestyramine) can only lower LDL cholesterol by approximately 25%. Therefore, bile acid sequestrants used alone are not as effective as statins in lowering LDL cholesterol.

Bile acid sequestrants are most useful in combination with a statin or niacin to aggressively lower LDL cholesterol levels. The combination of a statin and bile acid sequestrant can lower LDL cholesterol levels by approximately 50%. The combination of a statin and niacin can substantially reduce LDL cholesterol and elevate HDL cholesterol.

Bile acid sequestrants are not absorbed into the body, and therefore they do not have systemic side effects (affecting other organs). Their most common side effects are gastrointestinal and these include: 

• Constipation
• Abdominal pain
• Bloating
• Vomiting
• Diarrhea
• Weight loss
• Excessive passage of gas (flatulence)
• Heartburn
• Gallstones

Bile acid sequestrants can bind to and decrease the absorption (and hence the effectiveness) of other drugs, such as warfarin (Coumadin), thyroid hormones (Synthroid, Levoxyl), digoxin (Lanoxin), thiazide diuretics (Hydrodiuril, Oretic, Dyazide, Maxzide), and many others. Therefore, these medications should be taken 1 hour before or 4-6 hours after the administration of a bile acid sequestrant.

Bile acid sequestrants reduces the absorption of vitamin A, D, E, and K. Long-term use may thus cause a deficiency of vitamin A, D, E, and K.