A number of structural and microscopic changes occur as the liver ages. (See also Overview of the Liver and Gallbladder Overview of the Liver and Gallbladder Located in the upper right portion of the abdomen, the liver and gallbladder are interconnected by ducts known as the biliary tract, which drains into the first segment of the small intestine... read more for a discussion of normal function of the liver and gallbladder.) For example, the color of the liver changes from lighter to darker brown. Its size and blood flow decrease. However, liver test Liver Blood Tests Liver tests are blood tests that represent a noninvasive way to screen for the presence of liver disease (for example, hepatitis in donated blood) and to measure the severity and progress of... read more results generally remain normal.
The ability of the liver to metabolize many substances decreases with aging. Thus, some drugs are not inactivated as quickly in older people as they are in younger people. As a result, a drug dose that would not have side effects in younger people may have dose-related side effects in older people (see Aging and Drugs Aging and Medications Medications, the most common medical intervention, are an important part of medical care for older people. Without medications, many older people would function less well or die at an earlier... read more 
). Thus, drug dosages often need to be decreased in older people.
Also, the liver's ability to withstand stress decreases. Thus, substances that are toxic to the liver can cause more damage in older people than in younger people. Repair of damaged liver cells is also slower in older people.
The production and flow of bile decrease with aging. As a result, gallstones Gallstones Gallstones are collections of solid material (predominantly crystals of cholesterol) in the gallbladder. The liver can secrete too much cholesterol, which is carried with bile to the gallbladder... read more 
are more likely to form.
