In January, a vendor on Facebook advertising under the name Zhang Ellen peddled familiar fare: “good quality research chemicals” that included variants – or “analogues” – of fentanyl.

Some 50 times more potent than morphine, the drug has fuelled a synthetic opioids crisis in the US that in 2018 killed more than 30,000 people. After US-China trade talks included commitments by Beijing to crack down on its production in China, Trump administration officials now say the drug’s flow into the US has dramatically decreased.

Chinese vendors' ability to advertise publicly have also dwindled since tech companies, including social media platforms and e-commerce websites, improved their ability to trawl for fentanyl-related substances, said Logan Pauley, an analyst for Washington-based security research firm C4ADS who tracks the flow of synthetic opioids and other drugs into the US.

Now, amid a pandemic that has infected more than 900,000 worldwide and killed more than 46,000, Zhang’s Facebook feed today is flush not with fentanyl analogues but advertisements for hand sanitiser and face masks.

And when contacted privately, the vendor confirmed they were also selling both chloroquine and remdesivir, which could be sold at a “cheap price” for bulk orders. (Facebook did not respond to a request for comment.)

Pauley said he began to notice vendors advertising the antimalarial drugs online in mid-February – around the time chloroquine trials in China suggested possible efficacy of the drug against Covid-19, including one study the state news agency Xinhua said had found that chloroquine, remdesivir and another antiviral demonstrated “fairly good inhibitory effects” at the cellular level.

Other research in the country was less hopeful, with one small study in early March concluding that hydroxychloroquine, a variant of chloroquine, was no more effective than other forms of conventional care.

But demand for and prices of such drugs spiked in mid-March, when – contrary to what his own health officials were saying – Trump touted chloroquine, hydroxychloroquine, and remdesivir as possible “game changer” drugs against the coronavirus.

Misinformation and false claims in Trump’s responses to pandemic

At one White House briefing, Trump also wrongly claimed that his own Food and Drug Administration (FDA) had approved the deployment of chloroquine for use against Covid-19. The FDA has since issued an emergency use authorisation for it to be prescribed in certain situations while clinical trials continue.

Absent any clinical trial, “no magic drug” existed for coronavirus patients, Anthony Fauci, a top US health official, reminded the public during an appearance on CNN.

It was necessary, he said later at a briefing, to determine whether drugs like chloroquine would have any adverse effects when treating a patient with an ailment different from the one it was originally approved for.

And while not mentioning chloroquine or remdesivir by name, Tedros Adhanom Ghebreyesus, the head of the World Health Organisation (WHO), recently implored people to refrain from taking any drug that had not been shown to be safe or effective.

WHO warns countries not to treat Covid-19 patients with unproven drugs

Recent events have demonstrated the risk of self-medicating. In late March, an Arizona man died and his wife was hospitalised after ingesting fish-tank cleaner because it contained the same active ingredient as chloroquine. And in the Nigerian capital of Lagos, health authorities reported a rise in chloroquine poisoning following Trump’s remarks, according to Agence France-Presse.

Yet sale of the drugs by online vendors in China – many of which say their products are only for “research purposes” but have no way of knowing whether buyers use the chemicals themselves – has continued apace. Several companies indicated that they were struggling to keep up with the soaring demand.

A sales representative of one drug company based in Hebei province that recently started offering hydroxychloroquine expressed surprise at how much faith people seemed to place in Trump, who, the representative stressed, was “not a doctor”.

“If he said [the antibiotic] amoxicillin was an anticarcinogen, would everyone go to buy amoxicillin to treat cancer?” quipped the salesperson at Hebei Aicrowe Biotech Co, which sells products through e-commerce giant Alibaba’s international portal. (Alibaba is the parent company of the South China Morning Post.)

Amid the surge in interest, labs from which Aicrowe procured the chemicals had increased their prices “like crazy”, the salesperson said. The company was now selling hydroxychloroquine – entirely to customers overseas – at US$1,000 per kilogram.

Another vendor said that the company’s sale price of chloroquine, which was shipped mainly to US buyers, had increased tenfold since Trump’s remarks.

Despite the mark-up, the prices offered by Chinese vendors remain significantly lower than the typical cost of such drugs in the US. Without insurance, one 200mg pill of hydroxychloroquine sells at around 80 cents – equating to US$4,000 per kilogram – according to Drugs.com, an independent health care industry monitor.

Africans rush for chloroquine as coronavirus tsunami looms

The FDA, which advises Americans not to buy medication online from any pharmaceutical vendors based outside the US, referred inquiries to an agency notice stating that there are “currently no vaccines to prevent or drugs to treat Covid-19”.

In an open letter published last week, the agency emphasised that any substances listed for research purposes rather than consumption “have not been evaluated for safety in humans”.

When asked about the sale of chloroquine and remdesivir on its platform, a spokesperson for Alibaba cited a company policy that prohibits sellers from making any reference to Covid-19 or the coronavirus in product listings.

“We are now actively removing any such listings and taking punitive actions against sellers,” the spokesperson said.

While the pandemic has created a chance for many vendors in China to diversify their portfolios – and despite China’s tightening grasp on the production of fentanyl-related substances – many are still selling precursor substitutes, something that the US Drug Enforcement Administration (DEA) is actively trying to counter.

In a review of vendors offering chloroquine and remdesivir for overseas clients, the Post identified over a dozen – among them Aicrowe – also dealing in chemical substances that are either known analogues of fentanyl or precursors used in the production of the synthetic opioid.

Among its line-up, Aicrowe offered at least two known precursors to fentanyl: 40064-34-4 and 125541-22-2, as they are known according to their chemical abstracts service (CAS) numbers.

The latter is considered a “masked” precursor by the DEA, meaning that it must be subject to one or more chemical reactions before use in the synthesising process.

The extra degree of separation from the final product of fentanyl makes it difficult for US authorities to make a legal case for classifying such precursors controlled substances, said Pauley, who advises the US State Department’s bureau of international narcotics and drug enforcement.

When asked through Alibaba’s online chat portal about the likelihood that buyers were purchasing precursor chemicals for the production of fentanyl, Aicrowe’s sales representative said: “We don’t know – nor do we understand – what they use them for.”

“But if it breaks any law, then we don’t sell it,” the representative added, before blocking further inquiries.

How China’s opioid addicts get their drugs from an online black market

At least one other vendor selling chloroquine on Alibaba was also dealing in the chemical 99918-43-1, or “4-anilinopiperidine”, one of the fentanyl precursor substitute chemicals that the DEA proposed last year to have designated as controlled substances in the US.

The DEA, which argued in a Federal Register filing that the substance had no application “other than in the synthesis of fentanyl”, expected for the new controls to be adopted and publicly announced “in the very near future, possibly as early as next week,” an agency spokesman said.

The Alibaba spokesperson said the company prohibited the sale of any controlled substance, and also restricted “certain substances that are known to be precursor chemicals in the production of controlled substances”.

“We will continue to aggressively monitor our marketplace and welcome reports of any illicit listings to expedite takedowns,” the spokesperson said.

Following the Post’s inquiries about the sale of suspected fentanyl precursor substitutes on its platform, Alibaba began scrubbing listings of such chemicals from its English-language platform, including those listed by Aicrowe. As of Wednesday, a number of the same substances remained online on its Chinese platform.