Twelve people have been arrested across Greater Manchester for a string of drug and money laundering offences relating to the now illegal drug mephedrone.
Following raids at 11 addresses, seven men and five women were arrested as part of an investigation into online sales of the drug totalling more than £3.8m.
Police say 313kg (690lb) of the mephedrone, also known as m-cat or bubble, was sold via a website run from Bolton, with addresses also raided in the Bury and Salford areas of Greater Manchester as part of the operation.
Greater Manchester Police described the mephedrone crackdown as the largest of its kind in the UK since the drug became illegal in 2010.
Following the raids at the 11 properties, four men and five women aged between 21 and 62 have been arrested on suspicion of supplying controlled drugs and money laundering.
A man, aged 48, has been arrested on suspicion of the cultivation of cannabis and two men, aged 29 and 30, have been arrested on suspicion of possession with intent to supply.
Det Supt Jason Hudson said: "These strikes have taken months of planning and the operation reinforces our commitment to dismantle organised crime groups and tackle illegal drugs across our region.
"Our priority is to disrupt and prevent the supply of drugs and let this be a reminder to anyone involved in the supply, that they will not only end up behind bars, but through the Proceeds of Crime Act legislation, they will also end up out of pocket.
Chief supt David Hull, from Bolton division, said: "Cracking down on drugs in our communities is a big priority for GMP and I hope this operation shows communities we are committed to this.
"Drugs wreck lives and the crime associated with them cause misery to the whole community - so we do everything possible to find out who is responsible and put them before the courts."
The party drug mephedrone was legal to buy but not to consume until 2010.
Following outcry and warnings about dangers it poses to users' health, it is now illegal to supply or to be in possession of mephedrone under the Misuse of Drugs Act 1971.