Almost 10 million Americans say they misused opioid medications in 2012-2013, according to a new study from the National Institute on Alcohol Abuse and Alcoholism (NIAAA). Nonmedical use of prescription opioids more than doubled over a 10-year period, the study found.

The researchers found in 2012-2013, 4.1 percent of the adult population misused prescription opioids, compared with 1.8 percent in 2001-2002. This means they used the drugs without a prescription, or not as prescribed (in greater amounts, more often, or longer than prescribed) in the past year.

The study found that more than 11 percent of adults said they used prescription opioids nonmedically at some point in their lives, compared with 4.7 percent a decade earlier. In addition, 2.1 million adults meet the criteria for prescription opioid addiction.

“The increasing misuse of prescription opioid pain relievers poses a myriad of serious public health consequences,” Nora D. Volkow, MD, Director of the National Institute on Drug Abuse, said in a news release. “These include increases in opioid use disorders and related fatalities from overdoses, as well as the rising incidence of newborns who experience neonatal abstinence syndrome. In some instances, prescription opioid misuse can progress to intravenous heroin use with consequent increases in risk for HIV, hepatitis C and other infections among individuals sharing needles.”

People most likely to misuse opioids were men, those with annual incomes less than $70,000, those previously married, and with a high school education or less. Rates were higher among whites and Native Americans, and those living in the Midwest and West.

The study appears in the Journal of Clinical Psychiatry.

“Given the dramatic increase in nonmedical use of prescription opioids, it is important that clinicians and patients also recognize the potent interaction of opioids with alcohol and other sedative-hypnotic drugs – an interaction that can be lethal,” said NIAAA Director George F. Koob, PhD.