ABSTRACT To understand the magnitude of prescription opioid abuse in the United States, it is critical to determine how many dosage units of prescription opioids are ingested nonmedically per year. Using several public and private databases, the authors estimated that in 2002-2003, among the 10.89 million individuals projected to have used prescription opioids nonmedically, a minimum of 430.61 million doses were used nonmedically per year (assuming only one dose consumed per nonmedical use per day per individual). This represented about 1/25 of all prescription opioid doses dispensed. This estimate provides a perspective on the magnitude of prescription opioids abuse and should help policy makers enact policies that reduce prescription opioid abuse and diversion without preventing legitimate access to opioid therapy.