A flesh-eating drug and a potent heroin substitute has made its way to the United States, CNN reported.

Krokodil, an addictive injectable opiod that was first seen in Russia in 2003, allegedly turns its users into zombie-like creatures. Its side effects reportedly include black and scaly skin.

The Huffington Post reported the first confirmed case of krokidil was reported in the United States in 2012.

Two doctors from Missouri told the American Journal of Medicine they treated a patient last year "whose skin was rotted away from krokodil," the Raw Story reported.

"We saw that his finger fell off and we saw a severe looking ulcer and sores on his thigh and it did really fit the picture of krokodil," Dr. Dany Thekkemuriyil said. "Our case is the first case that's been published in a recognized medical journal."

A recent, but unconfirmed case of the drug surfaced in Arizona and has many in healthcare fields across the country on edge.

According to AZFamily, there are concerns that Arizona may be the epicenter of the deadly drug's U.S. invasion. At least two possible cases of the drug were reported to the Poison Control Center at Banner Good Samaritan Medical Center in Phoenix.

The calls to the poison control and medical center eventually led to a national alert.

"In [the first] case someone called and said we have a patient or two that may have used krokodil," Dr. Frank Lovecchio told AZFamily. "They claimed to have used krokodil."

After he received another call of the same nature, Lovecchio "sounded the alarm."

"When I heard of these cases, we did try to alert other physicians because we thought it was pretty serious -- you know, very life threatening," he said.

The Drug Enforcement Administration has not confirmed the Arizona cases were caused by krokodil. Other possible cases of krokodil have appeared in Illinois, Ohio and Oklahoma.

Lovecchio said krokodil is described as a drug that "eats users alive."

"They usually die of overwhelming skin infection," he said. "They usually die because they lose their limbs or extremities."

DEA Agent Ramona Sanchez told AZFamily the drug and its side effects are frightening enough to prompt an investigation.

"We start to monitor what chemicals are being used," she said. "We start to monitor who is doing it, and how it is being produced."