Hundreds of thousands of doses of unlicensed medicine have been seized as part of a regulator's "largest ever" crackdown on organised trafficking.
The Medicines and Healthcare products Regulatory Agency (MHRA) said 12 people were arrested during dawn raids across the West Midlands, Staffordshire, Greater Manchester and Merseyside on Tuesday.
The regulator said 150 officers were deployed for the raids, codenamed "Operation Subaru", searching 22 premises.
The suspects are being held for questioning by Staffordshire and Greater Manchester Police.
In the West Midlands region, properties were raided in Wolverhampton, Willenhall, Pattingham, Codsall and Wombourne North.
Controlled drugs such as opioid painkillers and anti-anxiety medicines were found during the searches, of both residential and commercial buildings.
In addition, officers seized about £100,000 in cash, luxury watches and suspected criminal assets held in cryptocurrency.
The MHRA said it had also obtained restraint orders for more than £3.5m in assets suspected to be linked to criminal activity.
The 12 individuals were arrested on suspicion of participating in the activities of an organised crime group, conspiracy to sell or supply controlled drugs and unlicensed medicines, and money laundering, the MHRA said.
Andy Morling, head of the regulator's criminal enforcement unit, said the raids followed "the largest investigation we've ever undertaken".
"Trafficking in medicines destroys lives and places a huge financial burden on wider society," he added.
"Our dedicated team will stop at nothing to tackle this illegal trade by taking potentially harmful medicines off the street and bringing those responsible to justice. As today's operation shows, there is nowhere to hide."
The MHRA worked with West Midlands and North West regional organised crime units and the National Crime Agency, alongside police.