The U.S. reached a grim milestone in April 2021: more than 100,000 Americans died of drug overdoses in a single year. The U.S. Centers for Disease Control and Prevention press release on this statistic said that opioids, especially the synthetic opioid fentanyl, drove the rise.

U.S. Rep. Beth Van Duyne, R-Irving,  tweeted Aug. 19: "Fentanyl is the leading cause of death among American adults."

The nation is grappling with a surge in opioid deaths, and there's no question that fentanyl is a key factor driving up those fatalities. Fentanyl is similar to morphine but is 50 to 100 times more potent, according to the National Institute on Drug Abuse. We reached out to Van Duyne's office to ask for her source for the statement but didn’t hear back. Van Duyne’s office did, however, provide an Associated Press fact check of a Families Against Fentanyl analysis that specified an age range for fentanyl-related deaths.

The advocacy group Families Against Fentanyl examined CDC data and determined fentanyl has become the leading cause of death for people ages 18 to 45 in 2019 and 2020. The group compared synthetic-opioid-related deaths with other major causes of death, which were listed in another CDC data set on leading causes of death.

Here’s what we know:

The CDC collects data revealing the leading causes of death in the U.S. In 2020, the leading causes of death among all American adults were heart disease, cancer, and COVID-19. Provisional data for 2021 showed these same health issues have continued as leading causes of death.

"Far more people die from cancer, heart disease and COVID-19, compared to fentanyl overdose," said Scott Walters, a professor of behavioral health at the University of North Texas Health Science Center at Fort Worth. Walters has been instrumental in work designed to address the opioid crisis in hard-hit communities in several states.

In 2020, more than 56,000 people ages 18 and older died in synthetic opioid-related incidents, according to data made available through the CDC’s online mortality database. In 2021, nearly 70,000 people 18 and older died in synthetic opioid-related incidents.

On whether fentanyl overdose is the leading cause of death for the 18-to-45 age range, a CDC spokesperson neither affirmed nor denied the statistic. 

Fentanyl-related deaths are coded as synthetic opioid-related deaths. Fentanyl comprises approximately 90% of the synthetic opioids category, the CDC said.

The spokesperson said "accidents (unintentional injuries)" was the leading cause of death in the age 18-to-45 group in 2021.

If one were to break out the unintentional injury category to make the drug categories rankable, the leading cause for people ages 18 to 45 would be unintentional drug overdose due to synthetic opioids. That number would exceed the second-highest leading cause of death (suicide in 2020 and COVID-19 in 2021.) 

In an email to PolitiFact Texas, the CDC spokesperson said, "If one assumes that the other synthetic narcotics category for those 18 to 45 is 90% fentanyl, then one can argue that unintentional fentanyl overdose is likely the leading cause in that age group.  However, because we don’t have exact numbers of fentanyl deaths for that age category, we cannot say for certain that this is accurate."

The spokesperson also noted overdose deaths are spread out across four different death categories: accidents, suicide, homicide and undetermined.

Public health advocates are sounding the alarm about opioids with good reason.

Scott Walters and researcher Joseph Friedman at the University of California, Los Angeles’ David Geffen School of Medicine told PolitiFact Texas synthetic opioid-related deaths is — or is likely — the leading cause of death for adults ages 18 to 45.

Brown University professor of epidemiology Brandon Marshall said drug overdose, as a broader category, is the leading cause of death among adults ages 18 to 45 with fentanyl playing a contributing role in most of them. Marshall cautioned, however, that many of these deaths are attributed to multiple substances, not solely fentanyl.

There are many ways to slice the data in the CDC database, experts said. Depending on which underlying causes of death are chosen in the database alongside the synthetic opioid cause-of-death code, the data can yield different numbers for the number of synthetic opioid-related deaths.

Michigan State University researcher Matthew Myers said synthetic opioids are the leading cause of death among adults ages 18 to 45. Data he pulled showed there are a higher number of synthetic opioid deaths other than methadone compared with firearm deaths, cardiovascular disease, motor vehicle accidents and cancer.

Dr. Lewis Nelson, chief of the Division of Medical Toxicology at Rutgers New Jersey Medical School and University Hospital, said it is plausible to say fentanyl overdoses are the leading cause of death for that age range, depending on how thinly you slice the information and data.

If you look at the data, you don’t see any cause of death category that comes near that level of synthetic opioid-related deaths, Nelson said.

You also could argue that this data, reported from death certificates, is an underestimate, Nelson said. Many jurisdictions across the country, staffed by coroners or medical examiners without a lot of funds, might not drug-test people who die.

"They might just put multidrug intoxication or something else, and that would not be counted as a fentanyl death," Nelson said.

However, Nelson said, if fentanyl is found in the body after death, then the death would be coded with synthetic opioids even if it is not the lethal agent. For example, if someone dies of a gunshot wound but also had fentanyl in their body, the synthetic opioids would be coded as an associated factor for the death.