Although the use of medication has helped to cure and control disease, it has also led to serious iatrogenic illness. Toxicity is most common and severe in the elderly. Confusion, falls, depression, sedation, deterioration of function, and urinary incontinence and retention are frequently the manifestation of that toxicity. Normal ageing places older patients at risk because of changes in metabolism, distribution, and excretion of drugs, and sensitivity to drug effects is often greater in the elderly. Disease and the interactions of other drugs can increase the incidence and severity of side effects. Certain drugs should be avoided in the elderly. Those that are long acting and require hepatic metabolism, those with strong anticholinergic properties, and those that are highly sedating tend to cause the most problems. In every case, physicians must weigh the potential benefit of prescribing against the potential risk.