Heroin use rose significantly over the past 11 years, according to a new report by the Substance Abuse and Mental Health Services Administration (SAMHSA).
In the past year, 681,000 Americans aged 12 and older used heroin.
Most people who used heroin were 26 or older, but an estimated 31,000 teens used heroin in 2013, the report found.
The number of people addicted to heroin rose from 214,000 in 2002 to 517,000 in 2013.
"Heroin use has reached alarming levels throughout our nation and we must work together to overcome this serious public health threat," SAMHSA Administrator Pamela S. Hyde said in a news release.
Between 2002 and 2007, an estimated 400,000 Americans used heroin. That number rose to 455,000 in 2008 and 582,000 in 2009, USA Today reports.
On average, every day about 460 Americans use heroin for the first time, according to SAMHSA.
The use of heroin is still relatively small compared with the use of marijuana and misuse of prescription drugs, the report notes.
About 13 percent of Americans 12 and older (33 million people) use marijuana, and 4 percent misuse prescription painkillers (11 million people).
The report noted, "Although research indicates that people who previously misused prescription pain relievers were more likely to initiate heroin use than people who had not misused prescription pain relievers, most people who misuse prescription pain relievers do not progress to heroin use."