The deadly drug carfentanil has exploded in recreational use in the United States, where it can be easily imported from China. The opioid is up to 50 times stronger than heroin and banned from the battlefield under the Chemical Weapons Convention. Since arriving on the scene in July, carfentanil has been blamed for hundreds of drug overdoses across the U.S. and been the subject of 400 documented cases of seizures, the Associated Press reported Thursday.

So what exactly is carfentanil and why is its use on the rise?

Controlled in the U.S., but Not in China

First produced in 1974 in the U.S., carfentanil was marketed under the brand name Wildnil. It is a controlled substance in the U.S. and intended only as a tranquilizer for large animals such as elephants. However, it is readily available in China. As many as 16 online companies were offering carfentanil for export to the U.S. and beyond for less than $3,000 per kilogram, an AP investigation discovered last month. One even bragged about it being a “hot sales product.”

Impact in the U.S.

In the U.S., carfentanil has been increasingly laced with heroin to form a deadly cocktail and adds to the already growing opioid epidemic across the country. The Drug Enforcement Agency warned that carfentanil can easily resemble both heroin and cocaine and urges individuals to use extreme caution. Early last month, Wayne County, Michigan, which includes the city of Detroit, reported 19 deaths associated with carfentanil since July. Similar reports have been occurring across the country, particularly in the Midwest.

Terrorism Threat

It is not just overdose deaths that have made officials in the U.S. concerned by the growing presence of carfentanil. After fentanyl, a related drug, was used by Russian forces against Chechen rebels who had taken hundreds of people hostage in a Moscow theater in 2002, the U.S. began working on strategies to counter its possible use by terrorists.

“Countries that we are concerned about were interested in using it for offensive purposes,” said Andrew Weber, assistant secretary of defense for nuclear, chemical and biological defense programs from 2009 to 2014, told the AP. “We are also concerned that groups like ISIS could order it commercially.”

Deadly Effects

In the Moscow theater siege, close to 200 people died after Russia pumped carfentanil into the theater, showing its deadly effects when simply ingested through the air. Indeed, it is the most potent opioid in commercial use, according to the DEA. Even a small amount absorbed through the skin can be deadly and law enforcement agencies have been warned about how to safely handle it. The DEA states that symptoms of exposure to the chemical include respiratory arrest, drowsiness, sedation, pinpoint pupils and clammy skin. The effects can begin within minutes of exposure. More than 10,000 times more potent than morphine, its lethal dose in humans is just two milligrams.

What to do if Exposed

Naloxone is the antidote for opioids, but, in the case of carfentanil exposure, it may take multiple doses to be effective, warns the DEA.