More than 131 million people — 66 percent of all adults in the United States — use prescription drugs. Utilization is particularly high for older people and those with chronic conditions. Prescription drugs are costly. Some $73 billion — almost 16 percent of total health care expenditures — was spent on prescription drugs for adults in 1998. Prescription drugs are a vital component of efforts to maintain or improve health. Advances in new products and technology and increases in utilization — the number of people using prescribed medicines and the number of prescriptions per user — have contributed to increases in overall prescription drug spending. The rising cost of prescription drugs affects everyone, but especially high prescription drug users, uninsured individuals, and health plans. Almost half of the cost of prescription drugs is paid out-of-pocket. Concerns about cost lead some consumers to take less than the prescribed medication.