Nineteen percent (n=190) reported non-medical prescription drug use in the previous 12 months. Across all sites, of those detainees who reported prescription drug use, benzodiazepines constituted the drug type most commonly used in the previous 12 months (65 percent). The next most commonly used type of prescription drug was opioids, which were used by 37 percent of those who had used prescription drugs illegally in the previous 12 months. Other drug types, such as antipsychotics and antidepressants were used by less than 10 percent of detainees who had reported pharmaceutical use in the previous 12 months. Prescription drug users were more likely than non-users in the total sample to be unemployed, derive their incomes from welfare or benefits, consider themselves drug dependent, be currently under a drug-related charge, and have been arrested or imprisoned in the previous 12 months. Of those who reported prescription drug use in the previous 12 months, 14 percent had used daily, 28 percent used once a week or more, 15 percent used monthly, 15 percent used every few months, and 29 percent used once or twice a year. Females were significantly more likely than males to have illegally used prescriptions drugs. Of the detainees who provided information on their prescription drug use, 24 percent had bought them from a dealer, 25 percent had bought them from a friend or relative, 43 percent had been given to them by a friend or relative without charge, and 7 percent had swapped them for another drug. 1 figure, 4 tables, and 14 references