Jennifer Trussell of the Office of Inspector General at the U.S. Department of Health and Human Services said some drug abusers get multiple prescriptions and sell what they don't use.
Some healthcare professionals write prescriptions or dispense drugs illegally, she said, while some criminals sell prescription drugs -- sometimes stealing patients' and providers' identities in the process.
"Prescription drug diversion is a clear health danger to everyone," Trussell said in a statement. "It's devastating to local communities, and is often fraud committed against our federal programs and the U.S. taxpayer.
"If you take prescription drugs, especially opioid painkillers, keep them in secure places, and watch your records for activity you didn't know about."