Older people tend to take more drugs than younger people because they are more likely to have several, often chronic disorders. On average, an older person takes four or five prescription drugs and two over-the-counter drugs each day. Also, older people are more than twice as susceptible to side effects of drugs as younger people (see Adverse Drug Reactions: Introduction). Side effects are also likely to be more severe, affecting quality of life and resulting in visits to the doctor and in hospitalization.

As people age, the amount of water in the body decreases and the amount of fat tissue relative to water increases. Thus, in older people, drugs that dissolve in water reach higher concentrations because there is less water to dilute them, and drugs that dissolve in fat accumulate more because there is relatively more fat tissue to store them. Also, as people age, the kidneys are less able to excrete drugs into the urine, and the liver is less able to metabolize many drugs (see Administration and Kinetics of Drugs: Metabolism). Because of all these age-related changes, many drugs tend to stay in an older person's body much longer than they would in a younger person's body, prolonging the drug's effect and increasing the risk of side effects. For these reasons, older people need to take smaller doses of certain drugs or perhaps fewer daily doses. Also, other, safer drugs can often be substituted.

Older people are more sensitive to the effects of many drugs. For example, older people tend to become sleepier and are more likely to become confused when using sleep aids or antianxiety drugs. Drugs that lower blood pressure by widening (dilating) arteries and reducing the amount of work the heart has to do tend to lower the pressure much more dramatically in older people than in the young.

Many commonly used drugs, such as some antidepressants and diphenhydramine (used in the treatment of insomnia), have anticholinergic effects. Older people are particularly susceptible to these effects, which include confusion, blurred vision, constipation, dry mouth, light-headedness, and difficulty with urination or loss of bladder control. Some anticholinergic effects, such as reduction of tremor (as in the treatment of Parkinson's disease) and reduction of nausea, are desirable, but most are not.

Drugs may produce a side effect because of interaction between the drug and a disease other than the one for which the drug is being taken (drug-disease interaction) or between the drug and another drug (drug-drug interaction), food (drug-food interaction), or a medicinal herb (drug-medicinal herb interaction (see Some Possible Medicinal Herb—Drug Interactions ). Because older people tend to have more diseases and to take more drugs than younger people, they are more likely to have drug-disease and drug-drug interactions. Patients, doctors, and pharmacists can take steps to reduce the risk of these interactions (see How to Reduce the Risk of Drug-Drug Interactions).

Not following a doctor's directions for taking a drug (noncompliance or nonadherence) can be risky (see Adherence to Drug Treatment). Old age alone does not make a person less likely to take drugs as directed; however, 40% of older people do not do so. Not taking a drug, taking too little, or taking too much can cause problems. Taking less of a drug because it causes side effects may seem reasonable, but people should talk to a doctor before they make any changes in the way they take a drug.

Some Drugs With Increased Risk for Older People Type Drug Problem Analgesics Indomethacin Of all the nonsteroidal anti-inflammatory drugs, indomethacin affects the brain the most. It sometimes causes confusion or dizziness.   Meperidine Meperidine, an opioid, is a strong analgesic when injected. But it is not very effective when taken orally and often causes confusion.   Pentazocine Pentazocine, an opioid, is more likely to cause confusion and hallucinations than are other opioids.   Propoxyphene Propoxyphene, an opioid, offers no more pain relief than acetaminophen. Like other opioids, it may be addictive and has such side effects as constipation, drowsiness, confusion, and (rarely) slowed breathing. Antidepressants Amitriptyline Doxepin Because amitriptyline and doxepin have strong anticholinergic and sedating effects, they are usually not good choices for older people. Antidiabetic drugs Chlorpropamide This drug has long-lasting effects, which are exaggerated in older people. It can lower blood sugar levels (hypoglycemia) for several hours. Chlorpropamide can also lower the level of sodium in the blood. Antiemetic drugs (drugs used to manage nausea) Trimethobenzamide This drug is one of the least effective drugs for managing nausea. It can produce side effects, including abnormal movements of the arms, legs, and other parts of the body. Antihistamines Chlorpheniramine Cyproheptadine Dexchlorpheniramine Diphenhydramine Hydroxyzine Promethazine Tripelennamine Some combination cold remedies All nonprescription and many prescription antihistamines have strong anticholinergic effects. Although sometimes helpful for managing allergic reactions and seasonal allergies, antihistamines are generally not appropriate for a runny nose and other symptoms of a viral infection in older people. When antihistamines are needed, those without anticholinergic effects (such as loratadine and astemizole) are preferable. Cough and cold remedies that do not include antihistamines are generally safer for older people. Older people should avoid taking sleep aids containing diphenhydramine. Antihypertensives Methyldopa Methyldopa, alone or in combination with other drugs, may slow the heart rate and worsen depression.   Reserpine Most experts in geriatric medicine believe that reserpine is risky because it can produce dizziness when a person stands up, depression, erectile dysfunction, and drowsiness. Antipsychotic drugs Chlorpromazine Haloperidol Thioridazine Thiothixene Although antipsychotics are effective in treating psychotic disorders, their effectiveness in treating behavioral disturbances associated with dementia (such as agitation, wandering, repeated questioning, noisiness, throwing, and hitting) has not been established. These drugs are commonly toxic, producing drowsiness, movement disorders, and anticholinergic effects. Generally, older people should take antipsychotics in small doses, if at all. The need for treatment should be reassessed often, and the drugs should be discontinued as soon as possible. Gastrointestinal antispasmodic drugs (drugs used to manage stomach cramps and pain) Belladonna alkaloids Clidinium-chlordiazepoxide Dicyclomine Hyoscyamine Propantheline Gastrointestinal antispasmodics are highly anticholinergic, and their usefulness—especially at the low doses tolerated by older people—is questionable. Heart drugs Digoxin Small doses should be used because as people age, the kidneys are less able to excrete digoxin.   Disopyramide Disopyramide, a drug used to treat abnormal heart rhythms (antiarrhythmic drug), has strong anticholinergic effects and may cause heart failure in older people. Histamine-2 (H2) blockers Cimetidine Famotidine Nizatidine Ranitidine Typical doses of some H2 blockers—especially cimetidine but, to some extent, famotidine, nizatidine, and ranitidine—may produce side effects, especially confusion. Iron supplements Ferrous sulfate Doses greater than 325 milligrams daily do not greatly improve absorption of iron and are much more likely to cause constipation. Muscle relaxants- antispasmodics Carisoprodol Chlorzoxazone Cyclobenzaprine Metaxalone Methocarbamol Oxybutynin Most muscle relaxant-antispasmodics have anticholinergic effects and cause drowsiness and weakness. the usefulness of all muscle relaxant-antispasmodics at the low doses tolerated by older people is questionable. Sedatives, antianxiety drugs, and sleep aids Barbiturates, such as phenobarbital and secobarbital Barbiturates have more side effects than other drugs used to treat anxiety and insomnia. They also interact with many other drugs. Generally, older people should not take barbiturates, except to treat seizure disorders.   Chlordiazepoxide Diazepam Flurazepam Nitrazepam These drugs are benzodiazepines used to treat anxiety and insomnia. They have very long-lasting effects (often more than 96 hours) in older people. Alone or in combination with other drugs, these drugs can cause prolonged drowsiness and increase the risk of falls and fractures. Shorter-acting benzodiazepines, such as alprazolam and lorazepam, are generally much more appropriate for older people.   Meprobamate This drug offers no advantages over benzodiazepines and has many disadvantages. It is very addictive and sedating.

Anticholinergic: What Does It Mean? Anticholinergic effects are caused by drugs that block the action of acetylcholine. Acetylcholine is a neurotransmitter—a chemical messenger released by a nerve cell to transmit a nerve signal to a neighboring nerve cell or a target cell in a muscle or gland. Acetylcholine stimulates smooth (involuntary) muscle cells, such as those in the heart or airways, to contract. Many commonly used drugs have anticholinergic effects. Most of these drugs were not designed to produce these effects, which are therefore usually considered undesirable side effects. Anticholinergic effects include confusion, blurred vision, constipation, dry mouth, light-headedness, and difficulty with urination or loss of bladder control. However, anticholinergic drugs can also, for example, reduce tremors and nausea—both useful effects. Older people are more likely to experience anticholinergic effects because the amount of acetylcholine in the body decreases with age. Consequently, anticholinergic drugs block a higher percentage of acetylcholine. Also, the aging body is less able to use what little acetylcholine is present.

Last full review/revision February 2003