These are the drugs killing the most people in the US

U.S. health officials are unpacking mortality data amid efforts to better understand the country's recent surge in drug overdose deaths, and a new report ranks the drugs that are most frequently involved in these fatalities.

Reflecting what's been described as America's opioid epidemic, the illegal drug heroin and prescription painkiller oxycodone both were at the top of the list for drug-related deaths in 2014, the latest year covered by the study.

But so also were cocaine and the anti-anxiety drug alprazolam, also known by brand names Xanax and Niravam.

Researchers from the Centers for Disease Control and Prevention and the Food and Drug Administration based the data on death certificate information that is typically written by medical examiners or coroners.

"The method was applied to provide a more in-depth understanding of the national picture of the drugs involved in drug overdose deaths," their study says.

The report shows that the number of drug overdose deaths and types of drugs involved in them varied within a short period. From 2010 to 2014, the number of overdose deaths in the U.S. increased by 23 percent, going from 38,329 in 2010 to 47,055 in 2014.

During that time, the rate of drug overdose deaths involving heroin more than tripled, the report says, while the rate of drug overdose deaths involving methamphetamine more than doubled.

Here is what the rankings looked like in 2010, when heroin and the opioid fentanyl had less of an impact on overdose deaths than in 2014. The researchers did urge caution in comparing numbers across years, however, as the rankings could be affected simply by improved reporting.

The upward trend in overdose deaths continued in 2015, with another CDC report published Friday showing that fentanyl and heroin use appeared to help drive an increase in overdose deaths that year.

Read more about drug issues plaguing the country:

53 PHOTOS
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

(Photo via Getty Images)

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

(Photo via Shutterstock)

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

(Photo via Shutterstock)

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

(Photo via Shutterstock)

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

(Photo via Getty Images)

Vermont

Deaths per 100,000: 12.9

(Photo by Denis Tangney Jr. via Getty Images)

South Carolina

Deaths per 100,000: 13

(Photo by Getty Images)

North Carolina

Deaths per 100,000: 13

(Photo via Getty Images)

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

(Photo via Getty Images)

United States average

Deaths per 100,000: 13.5

(Photo via Shutterstock)

Massachusetts

Deaths per 100,000: 13.7

(Photo via Corbis)

Florida

Deaths per 100,000: 13.9

(Photo via Alamy)

Washington

Deaths per 100,000: 14.1

(Photo via Getty Images)

Louisiana

Deaths per 100,000: 14.4

(Photo via Alamy)

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

(Photo via Getty Images)

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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