The emergence of tusi in South Florida and New York nightclubs and elsewhere complicates an increasingly unpredictable drug supply in the United States. Fentanyl, the synthetic opioid manufactured in clandestine Mexican labs and smuggled north, remains by far the nation’s most dangerous drug, even as fatal overdoses appear to have declined. Unbeknownst to some users of fentanyl, dealers mix in other synthetic drugs easily purchased online such as potent opioids known as nitazenes or the tranquilizer xylazine.

A senior Drug Enforcement Administration official warned that traffickers are capitalising on misperceptions that club drugs are safer. Tusi, the official said, is a “kind of kitchen-sink drug.”

“When you look at the lab results, they are throwing everything into this — which is just sort of reflective of where we are in the drug market,” said the official, speaking on condition of anonymity.

Versions of the drug emerged more than a decade ago in Colombia, where drug dealers dubbed it tusi as a phonetic translation of 2C, a class of psychedelics discovered in the late 1970s. Those psychedelics became popular in the US club scene in the 1990s and were sometimes sold as ecstasy, or MDMA.

Today, tusi rarely contains those psychedelic drugs, said Joseph Palamar, an epidemiologist at New York University Grossman School of Medicine who studies drug use. Instead, dealers appear to be capitalising on confusion and growing interest in psychedelics.

“I view it as a marketing scheme by drug dealers,” said Palamar, author of a paper last year in the American Journal of Drug and Alcohol Abuse warning about tusi.

Dealers dye the powders. Depending on the mix of uppers and downers, the effects can be unpredictable, especially if consumed with alcohol, Palamar said.

A New York electronic-music enthusiast in her late 30s who takes tusi when she parties on weekends said the drug enhances the music and lights on the dance floor.

“The energy feels good. It doesn’t last that long, and you’re not hung over the next day,” she said, speaking on condition of anonymity.

But she worries about consuming from a batch that is too potent or contains an unknown substance. “There are so many varieties. People make it different ways.”

The drug has already achieved celebrity infamy.

Multiple media outlets this week reported Payne, who died after falling from a balcony in Buenos Aires earlier this month, had multiple drugs in his system, including “pink cocaine”.

A March lawsuit alleged Combs arranged for the transport of tusi across state lines. Combs was arrested in September on allegations of sex trafficking that included plying women with ketamine, although a federal indictment does not name tusi. A federal prosecutor told a judge bags of pink powder were found in Combs’s New York hotel room when he was arrested.

Confusion about the drug emerged in the case of Maecee Marie Lathers, 24, of Miami Gardens, who described herself in social media posts as a model. Early on August 10, police and prosecutors said, she plowed her white Mercedes-Benz into two vehicles crossing an intersection near downtown Miami, resulting in two deaths.

She walked away, but was detained by witnesses, according to an arrest report. Officers found her lying on the pavement, bloodied and partially naked, screaming incoherently, according to police reports and body camera footage. Lathers said she was under the influence “and she was from the future and had a crystal ball,” an arrest report said.

Lathers is charged with driving under the influence manslaughter, among other offences, and has pleaded not guilty. A police arrest report and prosecutor court filing mistakenly refer to the drug as “2C,” the decades-old psychedelic drug. A toxicology report, released through a public records request, revealed Lathers had ketamine and MDMA in her blood.

The report revealed the alarming presence of another drug: fentanyl. It was unclear whether the tusi Lathers is suspected of ingesting was laced with fentanyl or if the opioid was consumed separately. Her defence lawyer declined to comment.

The test results illustrate the risk that drug dealers might add cheap fentanyl to batches sold as tusi, a possibly lethal combination if users lack opioid tolerance.

“I’ve been warning about this possibility for some time,” Palamar said. “Fentanyl entering the tusi supply could be disastrous.”

Palamar is collaborating with the Centre for Forensic Science Research & Education, a nonprofit toxicology organisation that runs an early-warning programme researching novel drugs, to test the saliva of New York clubgoers to understand what is in the drugs they are using.

Toxicologists at the Miami-Dade County Medical Examiner’s Office have linked brightly coloured powders found at death scenes to four suicides and four accidental overdose cases, the latter including famous DJ Erick Morillo, found dead inside his Miami Beach home, and aspiring singer Laura Camila Lozano Sterling, discovered dead inside an upscale Miami Beach hotel.

A ninth death involved a 28-year-old Chicago area man who had been using a pink powder and drinking with friends on a Miami Beach apartment balcony. According to medical examiner reports, he suddenly became paranoid — convinced someone was trying to kill him — and climbed atop the balcony before plummeting more than 15 metres. His death was ruled an accidental fall.

Each of them tested positive for ketamine, and most had MDMA and other drugs in their systems. More deaths may be associated with tusi. Toxicologists have identified about 50 other deaths involving ketamine and MDMA since 2018 but have not seen evidence of pink powders.

Ketamine, a drug commonly used to numb pain during surgeries and which is subject to state and federal restrictions, has been used recreationally for years. Its legal use has proliferated in recent years amid a boom in clinics and telehealth providers specialising in the drug’s potential to deliver rapid relief for people suffering from depression.

The drug prompts feelings of euphoria and sedation but can also act as a stimulant, medical experts say. At higher doses, ketamine’s effects can be severe.

“People who take a large amount of ketamine have problems with paranoia, delusions and hallucinations,” said Robert Freedman, a professor of psychiatry and pharmacology at the University of Colorado School of Medicine who has studied the effects of the drug.

Law enforcement officials worry cheap ketamine manufactured overseas could fuel the US market for tusi.

In recent years, federal agents at Miami International Airport have regularly arrested suspected smugglers from South America caught with premixed pink tusi hidden in bags or clothing. Sometimes, those couriers disembark from planes “pretty jacked up” on the drug, said Anthony Salisbury, special agent in charge of the Homeland Security Investigations South Florida field office.

“You look at their phone, and they’ve got little pink crystals because they were snorting on the plane,” Salisbury said.

The DEA has warned the Mexican Sinaloa Cartel — which has flooded the United States with fentanyl — is capable of importing vast amounts of ketamine from China to manufacture tusi. This year, a Coast Guard cutter found tusi among shipments of cocaine in the waters off Mexico and Central and South America.

Salisbury said investigators are concerned that because premixed tusi from South America is expensive — about US$100 ($165) a gram — domestic traffickers might be making their own batches with cheap ketamine and MDMA purchased from overseas through the mail.

That appears to be happening in New York, according to New York City Special Narcotics Prosecutor Bridget G Brennan, whose office recorded at least 40 seizures of ketamine or ketamine mixtures — stemming from 24 prosecutions — in 2023 and the first half of 2024. Investigators believe illicit ketamine was used to concoct colourful mixtures also seized in some cases.

“There’s nothing that I’ve seen that would indicate that it’s diverted” from legitimate stocks prescribed by doctors or used by veterinarians, Brennan said. “Most likely, it’s being imported.”