ARIZONA, USA (AP) — Aaron Francisco Chavez swallowed at least one of the sky blue pills at a Halloween party before falling asleep forever.

He became yet another victim killed by a flood of illicit fentanyl smuggled from Mexico into the Southwest — a profitable new business for drug gangs that has pushed the synthetic opioid to the top spot for fatal US overdoses.

Three others at the party in Tucson also took the pills nicknamed “Mexican oxy” and police flagged down by partygoers saved them by administering naloxone overdose reversal medication. But the treatment came too late for Chavez, who died at age 19.

The four thought they were taking oxycodone, a much less powerful opioid, investigators believe. The death of Chavez and many others, officials said, illustrate how Arizona and other southwestern states bordering Mexico have become a hot spot in the nation’s fentanyl crisis. Fentanyl deaths tripled in Arizona alone from 2015 through 2017.

“It’s the worst I’ve seen in 30 years, this toll that it’s taken on families,” said Doug Coleman, the US Drug Enforcement Administration special agent in charge of Arizona. “The crack (cocaine) crisis was not as bad.”

With plenty of pills and powder sold locally out of the arriving fentanyl shipments that are also distributed around the US, the drug that has surpassed heroin for overdose deaths has touched all Arizona demographic groups. Chavez’ family says he was working at a restaurant as a prep cook with dreams of becoming a chef and trying to turn his life around after serving prison time for a robbery conviction.

Also killed in the state over the last year by the pills that go for US$9 to US$30 each were a 17-year-old star high school baseball pitcher from a Phoenix suburb and a pair of 19-year-old best friends and prominent former high school athletes from the mountain town of Prescott Valley. The parents of one, Gunner Bundrick, said their son’s death left “a hole in our hearts”.

Popping the pills at parties “is a lot more widespread than we know”, said Yavapai County Sheriff’s Lt Nate Auvenshine. “There’s less stigma to taking a pill than putting a needle in your arm, but one of these pills can have enough fentanyl for three people.”

Stamped with “M”on one side and “30” on the other to make them look like legitimate oxycodone, the pills started showing up in Arizona in recent years as the Sinaloa cartel’s newest drug product, said Tucson Police Lt Christian Wildblood.

The fentanyl that killed Chavez was among 1,000 pills sneaked across the border crossing last year in Nogales, Arizona by a woman who was paid US$200 to tote them and gave two to Chavez at the party, according to court documents. It’s unknown if he took one or both.

At the same crossing last month, US officials announced their biggest fentanyl bust ever — nearly 254 pounds (115 kilogrammes) found in a truckload of cucumbers, enough to potentially kill millions. Valued at $3.5 million, most was in powder form and over two pounds (one kilogramme) was made up of pills.

The tablets in most cases are manufactured in primitive conditions with pill presses purchased online and the amount of fentanyl in each pill varies widely, Wildblood said.

The amount of fentanyl in counterfeit pills can vary from 0.03 to 1.99 milligrammes per tablet, or almost none to a lethal dose, according to the US Drug Enforcement Administration.

“There is no quality control,” Wildblood said.

While Chinese shipments were long blamed for illegal fentanyl entering the US, Mexico’s Army in November 2017 discovered a rustic fentanyl lab in a remote part of Sinaloa state and seized precursors, finished fentanyl and production equipment — suggesting some of it is now being synthesised across the US. border.

Most fentanyl smuggled from Mexico is about 10 per cent pure and enters hidden in vehicles at official border crossings around Nogales and San Diego, Customs and Border Protection data show. A decreasing number of smaller shipments with purity of up to 90 per cent still enter the US in packages sent from China.

Although 85 per cent of the fentanyl from Mexico is seized at San Diego area border crossings, the DEA’s 2018 National Drug Threat Assessment said seizures have surged at Arizona’s border and elsewhere around the state.

DEA statistics show Arizona fentanyl seizures rose to 445 pounds (202 kilogrammes), including 379,557 pills, in the fiscal year ending in October 2018, up from 172 pounds (78 kilogrammes), including 54,984 pills, during the previous 12-month period.

The Sinaloa cartel’s ability to ramp up its own production of fentanyl and label it oxycodone shows the group’s business acumen and why it remains among the world’s top criminal organisations, despite the conviction in New York this week of cartel kingpin Joaquin “El Chapo” Guzman Loera, Coleman said.