Age Infants and very young children are at special risk of adverse drug reactions because their capacity to metabolize drugs is not fully developed. Children under age 15 are at risk of Reye's syndrome if they are given aspirin while they have influenza or chickenpox. Some elderly people may be prone to confusion regarding instructions for the proper use of drugs. Elderly people who take drugs that may cause light-headedness, confusion, and impaired coordination are at risk of falling and fracturing a bone. Among the drugs that can cause such problems are many of the antihistamines, sleep aids, and antianxiety and antidepressant drugs.
Many drugs pose a risk to the normal development of a fetus.
To the extent possible, pregnant women shouldn't take drugs, especially during the first trimester. Other Factors Diseases can alter drug absorption, metabolism, and elimination and the body's response to drugs. Heredity may make some people more susceptible to the toxic effects of certain drugs. The realm of mind-body interactions, including such aspects as mental attitude, outlook, and belief in self and confidence in health care practitioners, remains largely unexplored. In general, the number and severity of adverse drug reactions increase as the dose increases.