For years, heroin has been the deadliest drug in Nashville. Not anymore.

It looks like just a few grains of salt, too small to taste, but hiding in these tiny white crystals is an unpredictable power to kill.

This is fentanyl, the new deadliest drug in Nashville.

Fentanyl killed more people than heroin in Davidson County for the first time ever last year, signaling that the core of the local opioid crisis has shifted to a new tier of powerful and dangerous drugs. As Tennessee has tightened its grip on prescription medication, many addicts have abandoned doctor shopping in favor of black market heroin and counterfeit pills that are often laced with fentanyl, a synthetic, cheap-to-produce, incredibly potent opioid that was once barely known outside of hospitals. For most people, two milligrams is a lethal dose.

“The streets are being flooded with fentanyl, and it’s contaminating these other drugs – whether they are heroin, or cocaine or counterfeit oxycodone,” said Dr. Howard Taylor, a toxicologist who has witnessed fentanyl spread through Nashville one blood test at a time. “It’s out there, it’s cheaper and it’s much more deadly.”

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In 2017, 105 people in Nashville suffered fatal overdoses with fentanyl in their bloodstream – four more than the overdose total for heroin – according to data released Wednesday by city police and the Metro Public Health Department. Although the margin between the death tolls is small, officials are most concerned about the swift rise of the fentanyl, which has spread through the city faster than heroin ever did. Fentanyl-related overdoses were nearly unheard of in Nashille only a few years ago, but deaths rose 250 percent in 2015, then 54 percent in 2016, and 75 percent in 2017.

Although alarming, experts described this rise as a predictable evolution of the opioid crisis, which shifts from pills to heroin to fentanyl, mostly as a result of simple economics. In a series of interviews with law enforcement, government officials and medical professionals, sources told The Tennessean that the fentanyl deaths show the opioid crisis had deepened to a new stage where drugs are cheaper to make, addiction is harder to stop and the risk of fatal overdose is far greater.

And death, it turns out, is no deterrent. Asked to explain the severity of the crisis, police and public health officials told the same story in separate interviews: When word gets out that a bad batch of fentanyl has killed a few people, many addicts don’t try to avoid it.

They go looking for it.

“From what we understand, the addicts want that,” said Rachel Franklin, a Metro Health official who coordinates responses to mass overdoses. “They want the biggest high they can find. They want to go the brink, and possibly get brought back with Narcan and not tip over that edge. It’s a crazy concept.”

“Two years ago, we thought we were going to come in and say ‘You don’t want this fentanyl stuff. It is deadly, even as small as a grain of sand.’” Franklin added. “But that is when they say – ‘Where is it?’

Tennessee's evolving crisis

Tennessee’s opioid crisis was primarily recognized in 2012 when it became widely known that pill abuse was rampant and that the state had one of the highest rates of pain medicine prescriptions in the nation. Many addictions began with legitimate ailments, but then patients began visiting multiple clinics to get redundant prescriptions, called "doctor shopping," to feed a growing dependence to opioids.

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Often, these addicts would later transition to heroin, which provides a similar high to prescription pills but can be bought in bigger doses for lower prices on the street. And as Tennessee lawmakers tightened restrictions on pain meds – for example, creating a database that checks patients for duplicate prescriptions – addicts found it was easier to acquire heroin than pills.

The next shift was almost inevitable. Where the heroin market grows, fentanyl is destined to follow.

Fentanyl is cheaper to make than heroin and as much as 50 times more potent, so some drug traffickers maximize their profits by selling weak heroin bolstered with fentanyl – a mixture that will kill if the fentanyl is not diluted enough. Dealers have also begun using fentanyl that has been strengthened at the chemical level, called "fentanyl analogues," which can be thousands of times more potent than heroin, said Tommy Farmer, special agent in charge of the Tennessee Bureau of Investigation’s drug division.

Fentanyl and fentanyl analogues hide in heroin like minuscule landmines, waiting to be stumbled upon by an unsuspecting addict. TBI also found fentanyl in cocaine for the first time last year, making the party drug – already notorious for overdoses – riskier than ever.

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“It's basically a matter of Russian Roulette, I don’t care what your tolerance is,” Farmer said. “You’ve got dealers with something as small as a gram that can potentially replace a kilo of heroin. There is no way they can get the doses right.”

In Nashville, Metro Police are now encountering fentanyl-laced heroin so frequently that street cops have been told not test heroin in the field so they don't accidentally inhale a dangerous dose on a windy day.

Sgt. Gene Donegan, of the Metro Police's Major Case Task Force, said the department is also on the lookout for carfentanil, a fentanyl analogue known to be 100 times stronger than regular fentanyl and 5,000 times stronger then heroin.

As absurd as it may sound, there is a demand, he said.

“To any any layperson, they would think ‘Holy cow I need to stay away from that,’” Donelson said. “But, to the addict, the first thing they think its that’s a more intense high then I’ve ever had.”

“And, unfortunately, it ends up killing them.”

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Fake oxycodone, real danger

Despite Tennessee's tighter restrictions on prescription pain pills, not all addicts make the jump to heroin. But that still doesn’t mean they are safe from fentanyl.

Farmer said the drug is frequently found in counterfeit oxycodone that is made with pill presses in rudimentary, black market drug labs. TBI busted 12 counterfeit operations last year, but fake pills continue to circulate the state, including throughout Nashville.

In a way, these pills can be more dangerous than heroin because buyers believe they are taking a professional product with familiar, standardized dosage.

In reality, the pills could be made of anything.

“Inside we find everything from heroin to fentanyl, aspirin to nothing, and chemicals that we don’t know what they are,” Farmer said. “But generally we don’t find the one thing they are looking for – oxycodone.”

Statewide, fentanyl deaths surpassed in heroin in 2016, showing that the progression of Nashville’s crisis is not unique in Tennessee. However, statewide overdose data from 2017 has not been released yet, so it is unclear if fentanyl is spreading through the state as fast as it is spreading in Nashville.

Brett Kelman is the health care reporter for The Tennessean. He can be reached at 615-259-8287 or at brett.kelman@tennessean.com.