New study suggests drugs are killing way more Americans than we thought

A new study suggests that the death toll from drug overdoses in America is much more severe than initially believed.

In December, the CDC said 52,404 people had died from drug overdoses in 2015, with over 60% dying from opioids (prescription painkillers) and heroin. Overdose numbers have been rising for years, but the new research, published Monday in the American Journal of Preventive Medicine, suggests that those rates were dramatically underreported.

The new paper posits that one reason for this gap is that in many overdose cases, no specific drug is identified as the cause on the death certificate. Data from 1999 to 2014 suggests that was the case up to one in four drug deaths recorded during that period.

RELATED: Drug overdose deaths per state

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Drug overdose deaths per state, 2015
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Drug overdose deaths per state, 2015

North Dakota

Deaths per 100,000: 2.7

(Photo by Ben Harding via Getty Images)

South Dakota

Deaths per 100,000: 6.4

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Nebraska

Deaths per 100,000: 7.3

(Photo via Getty Images)

Iowa

Deaths per 100,000: 8.7

(Photo via Getty Images)

Minnesota

Deaths per 100,000: 9.4

(Photo by Andrey Krav via Getty Images)

Virginia

Deaths per 100,000: 9.5

(Photo via Getty Images)

Texas

Deaths per 100,000: 9.8

(Photo via Getty Images)

New York

Deaths per 100,000: 10.6

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Mississippi

Deaths per 100,000: 10.7

(Photo via Getty Images)

Georgia

Deaths per 100,000: 10.8

(Photo via Alamy)

Kansas

Deaths per 100,000: 11.1

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California

Deaths per 100,000: 11.3

(Photo via Getty Images)

Hawaii

Deaths per 100,000: 11.8

(Photo by Richard Akuaten via Getty Images)

Maine

Deaths per 100,000: 11.9

(Photo by James Metcalf via Getty Images)

Illinois

Deaths per 100,000: 11.9

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Alabama

Deaths per 100,000: 12

(Photo by Rob Hainer via Getty Images)

Arkansas

Deaths per 100,000: 12.1

(Photo by Joe Sohm via Getty Images)

Oregon

Deaths per 100,000: 12.5

(Photo by Bob Pool via Getty Images)

Idaho

Deaths per 100,000: 12.8

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Vermont

Deaths per 100,000: 12.9

(Photo by Denis Tangney Jr. via Getty Images)

South Carolina

Deaths per 100,000: 13

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North Carolina

Deaths per 100,000: 13

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Wisconsin

Deaths per 100,000: 13.1

(Photo by Henryk Sadura via Getty Images)

New Jersey

Deaths per 100,000: 13.1

(Photo by Denis Tangney Jr. via Getty Images)

Connecticut

Deaths per 100,000: 13.1

(Photo by Sean Pavone via Getty Images)

Maryland

Deaths per 100,000: 13.4

(Photo by Sean Pavone via Getty Images)

Montana

Deaths per 100,000: 13.4

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United States average

Deaths per 100,000: 13.5

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Massachusetts

Deaths per 100,000: 13.7

(Photo via Corbis)

Florida

Deaths per 100,000: 13.9

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Washington

Deaths per 100,000: 14.1

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Louisiana

Deaths per 100,000: 14.4

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Michigan

Deaths per 100,000: 14.5

(Photo via Getty Images)

New Hampshire

Deaths per 100,000: 14.5

(Photo via Getty Images)

Washington, D.C.

Deaths per 100,000: 14.9

(Photo by Mark Segal via Getty Images)

Alaska

Deaths per 100,000: 15.3

(Photo by Sam Diephuis via Getty Images)

Colorado

Deaths per 100,000: 15.8

(Photo by David Parsons via Getty Images)

Indiana

Deaths per 100,000: 15.8

(Photo via Shutterstock)

Wyoming

Deaths per 100,000: 16.4

(Photo by Getty Images)

Missouri

Deaths per 100,000: 16.4

(Photo by Henryk Sadura via Getty Images)

Delaware

Deaths per 100,000: 17.2

(Photo by Ron Chapple via Getty Images)

Tennessee

Deaths per 100,000: 17.6

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Arizona

Deaths per 100,000: 18.1

(Photo via Getty Images)

Pennsylvania

Deaths per 100,000: 18.7

(Photo via Getty Images)

Ohio

Deaths per 100,000: 18.9

(Photo via Shutterstock)

Rhode Island

Deaths per 100,000: 19.6

(Photo via Kenneth C. Zirkel via Getty Images)

Oklahoma

Deaths per 100,000: 20.3

(Photo via Getty Images)

Utah

Deaths per 100,000: 21.9

(Photo via Getty Images)

Nevada

Deaths per 100,000: 22.4

(Photo by Andrew Zarivny via Shutterstock)

Kentucky

Deaths per 100,000: 24

(Photo via Getty Images)

New Mexico

Deaths per 100,000: 24.4

(Photo via Getty Images)

West Virginia

Deaths per 100,000: 32.4

(Photo by Stan Rohrer via Getty Images)

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However, even in cases in which no specific drug is listed as the cause of death, officials often do list at least one category of drug based on screenings they do at the time. For the latest study, the researchers used that information to correct the data they had on drug overdoses — and their findings were stark.

Nationally, corrected death rates from opioid painkillers were 24% greater than reported rates in 2014; those for heroin were 22% higher.

In the states where gaps between reported and actual death rates were greatest — Pennsylvania, Indiana, and Louisiana — the percentages differed by up to 108%.

These results change the face of the US' drug overdose epidemic substantially, as can be seen on the maps below. Reported overdose deaths for opioids and heroin are on the left; corrected deaths are on the right.

corrected opioid heroin mapsAmerican Journal of Preventive Medicine

The corrected figures suggest that deaths from opioids were much more concentrated in the Mountain states, Rust Belt, and Industrial North — extending to New England — as well as much of the South. Heroin deaths, on the other hand, were highest in the Northeast and Rust Belt states, but had less of an effect on the South or Mountain states.

"Current death certificate data are problematic for understanding the drug poisoning epidemic, with a particular issue being the frequency with which no specific drug is identified," wrote Christopher J. Ruhm, the author of the paper and a professor at the University of Virginia, in the paper.

The new analysis comes just four months after an investigation by a field officer for the Centers for Disease Control and Prevention also suggested that the death toll was higher than originally believed.

CDC field officer Victoria Hall and her Minnesota-based team reviewed a decade of death records submitted to the Minnesota Department of Health's Unexplained Death (UNEX) surveillance system.

RELATED: A look at the opioid and drug crisis in America

28 PHOTOS
Opioid and drug crisis in America
See Gallery
Opioid and drug crisis in America
Discarded needles are seen at a heroin encampment in the Kensington neighborhood of Philadelphia, Pennsylvania, on April 7, 2017. In North Philadelphia, railroad gulch as it is knowen, is ground zero in Philadelphia?s opioid epidemic. Known by locals as El Campanento, the open air drug market and heroin encampment is built with the discarded materials from the gulch and populated by addicts seeking a hit of heroin to keep their dope sick, or withdrawal symptoms, at bay. In one area, near the 2nd Avenue overpass, empty syringe wrappers blanket the refuse like grass the used needles they once contained poking through like thistles. / AFP PHOTO / DOMINICK REUTER (Photo credit should read DOMINICK REUTER/AFP/Getty Images)
NEW YORK, NY - JUNE 07: 'Surfer' shoots heroin in a park in the South Bronx on June 7, 2017 in New York City. Like Staten Island, parts of the Bronx are experiencing an epidemic in drug use, especially heroin and other opioid based drugs. More than 1,370 New Yorkers died from overdoses in 2016, the majority of those deaths involved opioids. The Mott Haven-Hunts Point area of the Bronx borough of New York currently leads the city in heroin overdose deaths. According to the Deputy Attorney General, drug overdose are now the leading cause of death for Americans under the age of 50. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JUNE 07: A man leans against the wall appearing to be under the influence of drugs on a street in the South Bronx on June 7, 2017 in New York City. Like Staten Island, parts of the Bronx are experiencing an epidemic in drug use, especially heroin and other opioid based drugs. More than 1,370 New Yorkers died from overdoses in 2016, the majority of those deaths involved opioids. The Mott Haven-Hunts Point area of the Bronx borough of New York currently leads the city in heroin overdose deaths. According to the Deputy Attorney General, drug overdose are now the leading cause of death for Americans under the age of 50. (Photo by Spencer Platt/Getty Images)
WASHINGTON, DC - SEPTEMBER 18: Family members of those who died of opioid overdoses attend the 'Fed Up!' rally to end the opioid epidemic on at the National Mall on September 18, 2016 in Washington, DC. Activists and family members gathered on the National Mall to march to the Capitol Building. Some 30,000 people die each year due to heroin and painkiller pill addiciton. Speakers called for Congress to provide $1.1 billion for the Comprehensive Addiction and Recovery Act, which Congress passed in July without funding. (Photo by John Moore/Getty Images)
NEW YORK, NY - JUNE 07: A man rests against a wall appearing to be under the influence of drugs on a street in the South Bronx on June 7, 2017 in New York City. Like Staten Island, parts of the Bronx are experiencing an epidemic in drug use, especially heroin and other opioid based drugs. More than 1,370 New Yorkers died from overdoses in 2016, the majority of those deaths involved opioids. The Mott Haven-Hunts Point area of the Bronx borough of New York currently leads the city in heroin overdose deaths. According to the Deputy Attorney General, drug overdose are now the leading cause of death for Americans under the age of 50. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JUNE 07: Brian smokes a synthetic drug called K2 on the street in the South Bronx on June 7, 2017 in New York City. Like Staten Island, parts of the Bronx are experiencing an epidemic in drug use, especially heroin and other opioid based drugs. More than 1,370 New Yorkers died from overdoses in 2016, the majority of those deaths involved opioids. The Mott Haven-Hunts Point area of the Bronx borough of New York currently leads the city in heroin overdose deaths. According to the Deputy Attorney General, drug overdose are now the leading cause of death for Americans under the age of 50. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JUNE 07: 'Surfer' shoots heroin in a park in the South Bronx on June 7, 2017 in New York City. Like Staten Island, parts of the Bronx are experiencing an epidemic in drug use, especially heroin and other opioid based drugs. More than 1,370 New Yorkers died from overdoses in 2016, the majority of those deaths involved opioids. The Mott Haven-Hunts Point area of the Bronx borough of New York currently leads the city in heroin overdose deaths. According to the Deputy Attorney General, drug overdose are now the leading cause of death for Americans under the age of 50. (Photo by Spencer Platt/Getty Images)
WASHINGTON, DC - SEPTEMBER 18: Activists and family members of loved ones who died in the opioid/heroin epidemic take part in a 'Fed Up!' rally at Capitol Hill on September 18, 2016 in Washington, DC. Protesters called on legistlators to provide funding for the Comprehensive Addiction and Recovery Act, which Congress passed in July without funding. Some 30,000 Americans die each year due to heroin and painkiller pill addiciton in the United States. (Photo by John Moore/Getty Images)
Quincy Massachusetts Police Detective Lt. Patrick Glynn holds a nasal injection containing the overdose-reversing drug naloxone at the police headquarters in Quincy, Mass., June 13, 2014. Quincy, Massachusetts, in 2010 became the first U.S. city to make the drug standard equipment for its police officers, who have used it to reverse some 275 overdoses, a significant number in a city of 93,000 people. Police forces nationwide are starting to follow suit. The state program has now moved far beyond police, training some 25,747 people in Massachusetts how to recognize the signs of opioid drug overdoses and administer naloxone. June 13, 2014. REUTERS/Gretchen Ertl (UNITED STATES - Tags: DRUGS SOCIETY HEALTH CRIME LAW)
A woman suspected of acting under the influence of heroine shows arms to police on April 19, 2017 in Huntington, West Virginia. Huntington, the city in the northwest corner of West Virginia, bordering Kentucky, has been portrayed as the epicenter of the opioid crisis. On August 15, 2016, from 3:00 pm to 9:00 pm, 28 people in the city overdosed on heroin laced with fentanyl, a synthetic opioid far more powerful and dangerous than heroin. The economic incentives are powerful: one kilogram of fentanyl costs $5,000, which can make a million tablets sold at $20 each for a gain of $20 million. 'This epidemic doesn't discriminate,' Huntington Mayor Steve Williams said. 'Our youngest overdose was 12 years old. The oldest was 77.' / AFP PHOTO / Brendan Smialowski / TO GO WITH AFP STORY by Heather SCOTT, US-health-drugs-WestVirginia (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
Paraphernalia for smoking and injecting drugs is seen after being found during a police search on April 19, 2017 in Huntington, West Virginia. Huntington, the city in the northwest corner of West Virginia, bordering Kentucky, has been portrayed as the epicenter of the opioid crisis. On August 15, 2016, from 3:00 pm to 9:00 pm, 28 people in the city overdosed on heroin laced with fentanyl, a synthetic opioid far more powerful and dangerous than heroin. The economic incentives are powerful: one kilogram of fentanyl costs $5,000, which can make a million tablets sold at $20 each for a gain of $20 million. 'This epidemic doesn't discriminate,' Huntington Mayor Steve Williams said. 'Our youngest overdose was 12 years old. The oldest was 77.' / AFP PHOTO / Brendan Smialowski / TO GO WITH AFP STORY by Heather SCOTT, US-health-drugs-WestVirginia (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
Paraphernalia for smoking and injecting drugs is seen after it was found during a police search on April 19, 2017, in Huntington, West Virginia. Huntington, the city in the northwest corner of West Virginia, bordering Kentucky, has been portrayed as the epicenter of the opioid crisis. On August 15, 2016, from 3:00 pm to 9:00 pm, 28 people in the city overdosed on heroin laced with fentanyl, a synthetic opioid far more powerful and dangerous than heroin. The economic incentives are powerful: one kilogram of fentanyl costs $5,000, which can make a million tablets sold at $20 each for a gain of $20 million. 'This epidemic doesn't discriminate,' Huntington Mayor Steve Williams said. 'Our youngest overdose was 12 years old. The oldest was 77.' / AFP PHOTO / Brendan Smialowski / TO GO WITH AFP STORY by Heather SCOTT, US-health-drugs-WestVirginia (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
Paraphernalia for injecting drugs is seen after being found during a police search on April 19, 2017 in Huntington, West Virginia. Huntington, the city in the northwest corner of West Virginia, bordering Kentucky, has been portrayed as the epicenter of the opioid crisis. On August 15, 2016, from 3:00 pm to 9:00 pm, 28 people in the city overdosed on heroin laced with fentanyl, a synthetic opioid far more powerful and dangerous than heroin. The economic incentives are powerful: one kilogram of fentanyl costs $5,000, which can make a million tablets sold at $20 each for a gain of $20 million. 'This epidemic doesn't discriminate,' Huntington Mayor Steve Williams said. 'Our youngest overdose was 12 years old. The oldest was 77.' / AFP PHOTO / Brendan Smialowski / TO GO WITH AFP STORY by Heather SCOTT, US-health-drugs-WestVirginia (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
Jessica, a homeless heroin addict, shows her kit of clean needles, mixing cap and tourniquet in the Kensington neighborhood of Philadelphia, Pennsylvania, on April 14, 2017. In North Philadelphia, railroad gulch as it is known, is ground zero in Philadelphia's opioid epidemic. 80 percent of us want to get out,' said Jessica, before outlining the numerous ways she has tried to get treatment for her addiction. In one case, she said, there weren't any available beds. In another, a treatment provider required a positive drug test before delivering aid, meaning if she hadn't used recently she'd be denied. Instead of getting treatment, she spends her nights trying to keep warm on a mattress under a bridge, the very spot where she was raped and infected with HIV. People come from throughout the city, and some as far away as the Midwest, for heroin that is remarkably cheap and pure at the largest heroin market on the East coast. / AFP PHOTO / DOMINICK REUTER (Photo credit should read DOMINICK REUTER/AFP/Getty Images)
Drug paraphernalia and other garbage litter a vacant house on April 19, 2017 in Huntington, West Virginia. Huntington, the city in the northwest corner of West Virginia, bordering Kentucky, has been portrayed as the epicenter of the opioid crisis. On August 15, 2016, from 3:00 pm to 9:00 pm, 28 people in the city overdosed on heroin laced with fentanyl, a synthetic opioid far more powerful and dangerous than heroin. The economic incentives are powerful: one kilogram of fentanyl costs $5,000, which can make a million tablets sold at $20 each for a gain of $20 million. 'This epidemic doesn't discriminate,' Huntington Mayor Steve Williams said. 'Our youngest overdose was 12 years old. The oldest was 77.' / AFP PHOTO / Brendan Smialowski / TO GO WITH AFP STORY by Heather SCOTT, US-health-drugs-WestVirginia (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
A man injects himself in the foot with heroin near a heroin encampmentin the Kensington neighborhood of Philadelphia, Pennsylvania, on April 14, 2017. In North Philadelphia, railroad gulch as it is known, is ground zero in Philadelphia's opioid epidemic. At the camp, and throughout the nearby area, a user can buy a bag of high-grade heroin at a low price and even pay to have another person inject them if for any reason they are unable to inject themselves. For several individuals, the addiction process was a slow one that started with a doctor's prescription for pain pills after an accident or surgery, and by the time the medication was finished, a dependency was born. After seeking black-market pills to feed their addiction, the simple economics of heroin won out: the price of a single pill could fetch anywhere between 2 and 10 bags of heroin, a savings that's hard to ignore when an insurance company is no longer underwriting the cost. / AFP PHOTO / DOMINICK REUTER (Photo credit should read DOMINICK REUTER/AFP/Getty Images)
WASHINGTON, DC - SEPTEMBER 18: Michael Botticelli, U.S. National Drug Control Policy Director, speaks at the 'Fed Up!' rally to end the opioid epidemic on September 18, 2016 in Washington, DC. Activists and family members of people who have died in the opioid and heroin epidemic gathered on the National Mall to march to the Capitol Building. Some 30,000 people die each year due to heroin and painkiller pill addiciton. Speakers called for Congress to provide $1.1 billion for the Comprehensive Addiction and Recovery Act, which Congress passed in July without funding. (Photo by John Moore/Getty Images)
A man uses a syringe to gather the last drops from a scavenged water bottle to mix up a shot of heroin near a heroin encampment in the Kensington neighborhood of Philadelphia, Pennsylvania, on April 14, 2017. In North Philadelphia, railroad gulch as it is known, is ground zero in Philadelphia?s opioid epidemic. The tracks and the surrounding property are owned and operated by the Consolidated Rail Corporation, a joint subsidiary of Norfolk Southern and CSX. People come from throughout the city, and some as far away as the Midwest, for heroin that is remarkably cheap and pure at the largest heroin market on the East coast. According to the city Health Commission, Philadelphia is on track to see 33 percent more drug overdose deaths in 2017 over last year. / AFP PHOTO / DOMINICK REUTER (Photo credit should read DOMINICK REUTER/AFP/Getty Images)
A Philadelphia Police officer patrols under a bridge near a heroin encampment in the Kensington neighborhood of Philadelphia, Pennsylvania, on April 14, 2017. In North Philadelphia, railroad gulch as it is known, is ground zero in Philadelphia��s opioid epidemic. The tracks and the surrounding property are owned and operated by the Consolidated Rail Corporation, a joint subsidiary of Norfolk Southern and CSX. Last month, Philadelphia Mayor Jim Kenney announced citations against the Consolidated Rail Corporation for what the mayor, in a release, said was Conrail's failure to clean and secure their own property.' Visitors and homeless residents of the gulch say the trash isn't their fault, and that they are only there because they have nowhere else to go. According to the city Health Commission, Philadelphia is on track to see 33 percent more drug overdose deaths in 2017 over last year. / AFP PHOTO / DOMINICK REUTER (Photo credit should read DOMINICK REUTER/AFP/Getty Images)
SANFORD, ME - FEBRUARY 16: Milo Chernin, who lost her son Sam to a heroin overdose on Jan. 16, 2017, looks at photos at her home in Sanford. She says that Sam, who died at age 25, struggled with his addiction and could not stay away from heroin despite getting treatment. (Photo by Derek Davis/Portland Press Herald via Getty Images)
WASHINGTON, DC - SEPTEMBER 18: Activists and family members of loved ones who died in the opioid/heroin epidemic take part in a 'Fed Up!' rally at Capitol Hill on September 18, 2016 in Washington, DC. Protesters called on legistlators to provide funding for the Comprehensive Addiction and Recovery Act, which Congress passed in July without funding. Some 30,000 Americans die each year due to heroin and painkiller pill addiciton in the United States. (Photo by John Moore/Getty Images)
GROTON, CT - MARCH 23: A box of the opioid antidote Naloxone, also known as Narcan, sits on display during a family addiction support group on March 23, 2016 in Groton, CT. The drug is used to revive people suffering from heroin overdose. The group Communities Speak Out organizes monthly meetings at a public library for family members to talk about how their loved ones' addiction affects them and to give each other emotional support. Communities nationwide are struggling with the unprecidented heroin and opioid pain pill epidemic. On March 15, the U.S. Centers for Disease Control (CDC), announced guidelines for doctors to reduce the amount of opioid painkillers prescribed nationwide, in an effort to curb the epidemic. The CDC estimates that most new heroin addicts first became hooked on prescription pain medication before graduating to heroin, which is stronger and cheaper. (Photo by John Moore/Getty Images)
NEW LONDON, CT - MARCH 23: A heroin user injects himself on March 23, 2016 in New London, CT. Communities throughout New England and nationwide are struggling with the unprecidented heroin and opioid pain pill epidemic. On March 15, the U.S. Centers for Disease Control (CDC), announced guidelines for doctors to reduce the amount of opioid painkillers prescribed nationwide, in an effort to curb the epidemic. The CDC estimates that most new heroin addicts first became hooked on prescription pain medication before graduating to heroin, which is stronger and cheaper. (Photo by John Moore/Getty Images)
GROTON, CT - MARCH 23: Family members of people addicted heroin and opioid pain pills share stories during a support group on March 23, 2016 in Groton, CT. The group Communities Speak Out organizes monthly meetings at a public library for family members to talk about how their loved ones' addiction affects them and to give each other emotional support. Communities nationwide are struggling with the unprecidented heroin and opioid pain pill epidemic. On March 15, the U.S. Centers for Disease Control (CDC), announced guidelines for doctors to reduce the amount of opioid painkillers prescribed nationwide, in an effort to curb the epidemic. The CDC estimates that most new heroin addicts first became hooked on prescription pain medication before graduating to heroin, which is stronger and cheaper. (Photo by John Moore/Getty Images)
NEW LONDON, CT - MARCH 14: Jackson, 27, who said he is addicted to prescription medication, lies passed out in a public library on March 14, 2016 in New London, CT. Police say an increasing number of suburban addicts are coming into the city to buy heroin, which is much cheaper than opioid painkillers. On March 15, the U.S. Centers for Disease Control (CDC), announced guidelines for doctors to reduce the amount of opioid painkillers prescribed nationwide. The CDC estimates that most new heroin addicts first became hooked on prescription pain medication before graduating to heroin, which is stronger and cheaper. (Photo by John Moore/Getty Images)
ST. JOHNSBURY, VT - FEBRUARY 06: 'Buck' who is 23 and addicted to heroin, shoots up Suboxone, a maintenance drug for opioid dependence that is also highly addictive on February 6, 2014 in St. Johnsbury, Vermont. Vermont Governor Peter Shumlin recently devoted his entire State of the State speech to the scourge of heroin. Heroin and other opiates have begun to devastate many communities in the Northeast and Midwest leading to a surge in fatal overdoses in a number of states. As prescription painkillers, such as the synthetic opiate OxyContin, become increasingly expensive and regulated, more and more Americans are turning to heroin to fight pain or to get high. Heroin, which has experienced a surge in production in places such as Afghanistan and parts of Central America, has a relatively inexpensive street price and provides a more powerful affect on the user. (Photo by Spencer Platt/Getty Images)
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Hall, who presented the results on Monday at a CDC conference, found that of the 1,676 UNEX deaths between 2006 and 2015, approximately 3.5% had some complications due to opioid use. Those deaths were never filed as opioid-related deaths, despite some autopsies showing toxic or even lethal levels of painkillers.

That's likely because the CDC classifies deaths using codes dictated by the Center's International Classification of Diseases. In some cases, if a person died due to an infectious disease, such as pneumonia, the death was classified for that only that condition, even if opioids were seen as a significant contributing factor.

"While my research cannot speak to what percent we are underestimating, we know we are missing cases," Hall told CNN. "It does seem like it is almost an iceberg of an epidemic."

BI Graphics_Drug OverdosesSkye Gould/Business Insider

The UNEX system, which began in 1995, originally included other states as well, but Minnesota is the only one that's currently maintaining its system.

Minnesota is far from the hardest-hit state in the opioid crisis, however — its overdose death rate ranks 45th in the US.

According to Hall, there is no national standard for how to file a death certificate or for what constitutes an overdose, leaving much to a medical examiner's discretion.

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