More than six tonnes of 1,4-Butanediol - commonly known as bute - worth an estimated $132 million on the street was seized from post offices and storage units across Sydney in a series of raids.
Local police on Tuesday stopped a 27-year-old as he was driving in the city's west and seized about 110kg of the chemical, which has frequently been linked to sexual assaults.
Investigators later raided a storage facility, where they found 6.3 tonnes of bute distributed across 500 boxes, which were packed with falsely labelled bottles that contained the substance in liquid form.
Bute is an industrial solvent the body naturally converts into gamma-hydroxybutyrate, also known as liquid ecstasy, which slows down the brain's messaging to the body and nervous system.
While the chemical has legitimate uses, it has also been linked to drink-spiking incidents due to it causing drowsiness and leading to a loss of inhibitions.
Warehouses and post offices played a crucial role in the discovery of the trove of the chemical, which was made a border-controlled drug in early 2024.
NSW Police Assistant Commissioner Gavin Wood said it was one of the state's largest busts involving the chemical.
"The standard postal system is part of the equation (and) how the drugs arrived in the country is part of the investigative probe," he said on Thursday.
Officers conducting a firearms order check found a parcel containing about five litres of bute that had been sent from a storage facility.
It was seized for forensic examination, prompting police to set up a strike force.
Police later found 225kg of bute at a postal facility and then another 23 litres believed to be bute at a nearby post office.
That led to the driver's arrest and the multi-tonne haul from the single storage facility.
"It is in some respects a rarity, a smaller job leading to such a huge job," Mr Wood said.
The man and a 28-year-old woman were both charged with supplying a large, commercial quantity of a prohibited drug.
Both are due to face Burwood Local Court on Thursday.
The offence carries a maximum sentence of life in prison.
Bute is commonly used in the illicit party drug known as "fantasy", but Mr Wood said he could not speculate on how the six-tonne haul would have been sold.
The latest raids follow a series of seizures involving federal authorities, who in May said they had stopped the illegal importation of 4200 litres of bute in just three months.
Imports of the drug from the Asian market, particularly China, had ramped up in recent years, Australian Border Force officials said.
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