Fentanyl, a synthetic opioid painkiller, made up almost half of drug overdose deaths in parts of the St. Louis region last year, according to county coroners in Missouri and Illinois.

The drug is up to 50 times more powerful than heroin, and inhaling just a few grains can be lethal.

“If I can be blunt, it’s scary as hell,” said Brandon Costerison, a spokesperson for the anti-addiction group NCADA's St. Louis chapter. “And we don’t really have anything to indicate it’s subsiding yet.”

In Madison County, the number of fentanyl-related deaths tripled from 2015 to 2016, while deaths attributed to heroin declined. Often, the drugs are mixed. Some cases were attributed to carfentanil, an illicit fentanyl-related compound that is even more powerful.

“It’s our firm belief that these fentanyl deaths were because heroin addicts were being delivered this drug on the premise that it was heroin,” County Coroner Steve Nonn said.

Though fentanyl is used in clinical settings, the Drug Enforcement Administration issued a warning in December that dealers are smuggling counterfeit forms of the drug into the United States.

In St. Louis, about a dozen people died after taking fentanyl or fentanyl-related drugs in 2014.

Two years later, that death count reached 151, roughly half of the city’s total drug overdoses in 2016.

“When you buy from a street corner drug dealer you have no earthly idea what you’re getting — either what drug you’re getting or how much,” said Dr. Michael Graham, St. Louis’ chief medical examiner. “People take what they used to take, and it results in a massive overdose.”

According to the Centers for Disease Control and Prevention, states in the Midwest saw a higher than average increase in overdose deaths due to synthetic opioids between 2014 and 2015, particularly in Illinois. Local numbers suggest that trend is continuing.

From NPR: Deaths involving fentanyl rise as curbing illicit supply proves tough

Police departments, fire stations and ambulance corps in the St. Louis area have stocked first responders with naloxone, an emergency drug that can reverse an overdose. The St. Louis Fire Department used it 1,900 times last year, according to the St. Louis Post-Dispatch.

State lawmakers in Missouri are considering a “Good Samaritan” law to grant immunity from some drug charges if a person calls 911 to save someone from an overdose. Another bill would establish a monitoring database for physicians and pharmacists to track opioid prescriptions. Missouri is the only state without such a program, though St. Louis County is implementing a limited version on its own.

Nonn, the Madison County coroner, said he will start to see hope in the opioid crisis when he sees people responding to it as a public health issue, not a criminal issue.

“You cannot arrest your way out of this problem," Nonn said. "It has to be a total shift in the way we handle these opioids in America.”

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Note: Most 2016 numbers are preliminary, and total drug overdose deaths for three counties were unavailable. Coroners' annual reports are generally published in the summer.