Resins, including colestipol, cholestyramine and colesevelam, are pharmacological agents used for the treatment of hyperlipidemia. They are useful only for isolated increases in LDL, and may further increase VLDL levels in patients with hypertriglyceridemia. These drugs are very useful in combination, especially with statins.
These agents have positive charges, and so bind negatively charged bile acids in the small intestine to prevent their reabsorption. The result is a tenfold increase in excretion, and enhanced conversion of cholesterol to bile acids in the liver. The resin itself is also not absorbed. The overall effect of the drug is a decrease in LDL.
Common side effects are constipation and bloating, usually relieved by increasing dietary fiber or mixing psyllium seed with the resin.