The annual number of U.S. drug overdose deaths has been growing for more than 20 years. Officials have been most worried about a class of powerful prescription "opioid" painkillers like Vicodin and OxyContin. Deaths involving such painkillers continue to be much more common than heroin-related deaths, the study found.
But while those deaths are levelling off or declining in many parts of the country, heroin-related deaths soared between 2010 and 2012 in the 28 states for which information was available to the researchers.
Heroin overdose deaths rose from 1,779 to 3,665, doubling the death rate to 2.1 deaths per 100,000 people.
Heroin-related deaths increased in both men and women, in all age groups, and in whites, blacks and Hispanics.
Officials say the trend's future is hard to predict. "It's a volatile situation," said one of the study's authors, Dr. Len Paulozzi of the Centers for Disease Control and Prevention.
The study looked at 2012 overdose death data from death certificates and compared it to 2010. The 28 states sampled include more than half of the U.S. population and account for more than half of the nation's drug overdose deaths.
Overdose numbers from all the states are not expected to be released for at least a few more months.
While the heroin death toll doubled, deaths linked to opioid painkillers fell in the 28 states, from 10,427 in 2010 to 9,869 in 2012. The death rate declined to 5.6 per 100,000.
Why the jump in heroin-related deaths as opioid painkiller deaths declined? Recent restrictions on prescribing opioid painkillers may be reducing illicit supplies of them at a time when the heroin supply has been increasing, experts said.
The main reason may be that people who had been abusing the painkillers moved "from high-priced pills to more affordable heroin," Barbara Carreno, a spokeswoman for the U.S. Drug Enforcement Administration, wrote in an email.
A possible indicator of heroin's growing supply: The DEA's domestic seizures of the drug rose from around 1,300 pounds a year in 2007-2009 to roughly 2,200 pounds annually in 2011-2013, she said.
"There is heroin around and people do try it," said Dr. Hillary Kunins, assistant commissioner at the New York City's health department.
The heroin problem has been dramatic in New York City — a place where about two people die of fatal drug overdoses every day, on average.
Through the last decade, heroin-related deaths remained more common in New York than opioid painkiller-related deaths. In 2013, heroin overdose caused 6.2 deaths per 100,000 New Yorkers, the highest rate in a decade.