Investigators who nicknamed the mixture have detected it or recorded overdoses blamed on it in Alabama, Georgia and Ohio.

COLUMBUS, Ohio —

It's being called "gray death" — a new and dangerous opioid combo that underscores the ever-changing nature of the U.S. addiction crisis.

Investigators who nicknamed the street mixture have detected it or recorded overdoses blamed on it in Alabama, Georgia and Ohio. The drug looks like concrete mix and varies in consistency from a hard, chunky material to a fine powder.

The substance is a combination of several opioids blamed for thousands of fatal overdoses nationally, including heroin, fentanyl, carfentanil — sometimes used to tranquilize large animals like elephants — and a synthetic opioid called U-47700.

"Gray death is one of the scariest combinations that I have ever seen in nearly 20 years of forensic chemistry drug analysis," Deneen Kilcrease, manager of the chemistry section at the Georgia Bureau of Investigation, said.

Gray death ingredients and their concentrations are unknown to users, making it particularly lethal, Kilcrease said. And because these strong drugs can be absorbed through the skin, simply touching the powder puts users at risk, she said.

Last year, the U.S. Drug Enforcement Administration listed U-47700 in the category of the most dangerous drugs it regulates, saying it was associated with dozens of fatalities, mostly in New York and North Carolina. Some of the pills taken from Prince's estate after the musician's overdose death last year contained U-47700.

Gray death has a much higher potency than heroin, according to a bulletin issued by the Gulf Coast High Intensity Drug Trafficking Area. Users inject, swallow, smoke or snort it.

Georgia's investigation bureau has received 50 overdose cases in the past three months involving gray death, most from the Atlanta area, said spokeswoman Nelly Miles.

In Ohio, the coroner's office serving the Cincinnati area says a similar compound has been coming in for months. The Ohio attorney general's office has analyzed eight samples matching the gray death mixture from around the state.

The combo is just the latest in the trend of heroin mixed with other opioids, such as fentanyl, that has been around for a few years.

Fentanyl-related deaths spiked so high in Ohio in 2015 that state health officials asked the federal Centers for Disease Control and Prevention to send scientists to help address the problem.

The mixing poses a deadly risk to users and also challenges investigators trying to figure out what they're dealing with this time around, said Ohio Attorney General Mike DeWine, a Republican.

"Normally, we would be able to walk by one of our scientists, and say 'What are you testing?' and they'll tell you heroin or 'We're testing fentanyl,'" DeWine said. "Now, sometimes they're looking at it, at least initially, and say, 'Well, we don't know.'"

Some communities also are seeing fentanyl mixed with non-opioids, such as cocaine. In Rhode Island, the state has recommended that individuals with a history of cocaine use receive supplies of the anti-overdose drug naloxone.

These deadly combinations are becoming a hallmark of the heroin and opioid epidemic, which the government says resulted in 33,000 fatal overdoses nationally in 2015. In Ohio, a record 3,050 people died of drug overdoses last year, most the result of opioid painkillers or their relative, heroin.

Most people with addictions buy heroin in the belief that's exactly what they're getting, overdose survivor Richie Webber said.

But that's often not the case, as he found out in 2014 when he overdosed on fentanyl-laced heroin. It took two doses of naloxone to revive him. He's now sober and runs a treatment organization, Fight for Recovery, in Clyde, about 45 miles (72 kilometers) southeast of Toledo.

A typical new combination he's seeing is heroin combined with 3-methylfentanyl, a more powerful version of fentanyl, said Webber, 25. It's one of the reasons he tells users never to take drugs alone.