Last month, Eloise Aimee Parry, a 21-year-old student from Shropshire, died after taking "diet pills" she purchased on the internet.
Now, Interpol has issued a global alert over the threat posed by the pills.
The world police agency has raised the alarm with forces in 190 countries after the toxic pesticide dinitrophenol was linked to the death of Parry and also left a Frenchman critically ill.
Police believe the pills Parry purchased online included a quantity of the substance, known as DNP.
A study last year warned the drug, sometimes used as a weight loss or bodybuilding aid, could be linked to five more deaths in the UK between 2007 and 2013 and could cause breathing difficulties, fast heart rates, fever, nausea and vomiting.
In an Orange Notice issued by Interpol, at the request of French health authorities, the agency declared an "imminent threat" to consumers from DNP, which has also been used in explosives.
Online distributors have even tried to mask its supply from customs and police officers by labelling it as the yellow spice turmeric because it looks similar, Interpol said.
A statement from the agency added: "Although usually sold in yellow powder or capsule form, DNP is also available as a cream. Besides the intrinsic dangers of DNP, the risks associated with its use are magnified by illegal manufacturing conditions.
"In addition to being produced in clandestine laboratories with no hygiene regulations, without specialist manufacturing knowledge the producers also expose consumers to an increased chance of overdose."
The alert came after the World Anti-Doping Agency (Wada) analysed a sample seized in Australia, prompting fears it has become widely available on the black market again, having been withdrawn in the 1930s and again in the 1980s following related deaths.
Wada's director general David Howman said: "We are appreciative that Interpol has issued this global warning on DNP.
"This is a perfect example of how crucial it is that law enforcement and anti-doping organisations continue to forge closer ties so that dangerous, and potentially fatal, substances such as DNP do not reach the hands of athletes."
Parry's mother Fiona has also warned others to avoid the chemical.
"My message would be please don't, please don't take this drug," she said. "They will take their toll and it is an awful way to die."