Marcelo is an illiterate 24-year-old drug addict whose home is a sliver of cardboard on the streets of Rio Branco, a riverside city in the Brazilian Amazon. His drug of choice is oxi, a highly addictive and hallucinogenic blend of cocaine paste, gasoline, kerosene and quicklime (calcium oxide) that is wreaking havoc across the Amazon region.

Oxi, or oxidado – “rust” – is the latest drug to surface in the Amazon. It is reputedly twice as powerful as crack cocaine and just a fifth of the price.

“It is terrifying,” said Alvaro Mendes, an outreach worker in Rio Branco from the state of Acre’s Harm Reduction Association, the NGO that first detected the drug. “The majority of first-time users become addicted on their first contact with the drug. Most of them go seven to 10 days without sleeping, without eating. They start to go into a process of degeneration. After months of use … they go into a state where they look like zombies, wandering … in search of pleasure.”

Described as a cheaper and deadlier successor to crack, oxi sells for about R$2 (75p) a rock and is smoked in pipes improvised from cans, pieces of piping and metal taps. According to Mendes, whose support group works with slum-dwellers, prostitutes, transvestites and homeless people who are hooked on the drug, oxi can kill within a year.

“The difference between cocaine and oxi is like the difference between drinking beer and pure alcohol,” said a federal police operative on the Peru-Brazil border, who refused to be named.

Oxi surfaced in the Amazonian border region between Brazil, Bolivia and Peru in the 1980s, and is said to have been originally used by a small number of hippies who came to the region to experiment with ayahuasca, a hallucinogenic plant native to the Amazon rainforest.

In the past five years, however, its use has exploded, particularly in the slums and rural communities of Acre state in the western Amazon, where it is peddled in street-corner drug dens known as bocadas. Mendes estimates there are at least 8,000 oxi users in Acre’s capital, Rio Branco, a city of 320,000 inhabitants.

But oxi is no longer just an Amazonian drug. A series of recent suspected seizures in cities such as Sao Paulo, Brasilia and Rio de Janeiro have propelled it into the national headlines. Health workers and politicians warn of a catastrophe if its spread is confirmed.

“The Brazilian state is unprepared to face this threat and to help its victims,” José Serra, a leading opposition politician and former governor of Sao Paulo, wrote in a recent column in the national daily Estado de Sao Paulo, describing oxi on his Twitter account as a “weapon of mass destruction”.