A vast international police operation involving 33 countries and the World Anti-Doping Agency has seized millions of doping substances and counterfeit medicines and arrested 234 people, Europol said on Monday.

The operation involving 23 European Union nations and 10 other countries, including Albania, Colombia, Iceland, Switzerland and the United States, seized 3.8 million illegal medicines, a statement said.

The World Anti-Doping Agency (WADA) said the operation “dismantled 17 organised crime groups involved in the trafficking of counterfeit medicines and doping material across Europe.”

The Europol-coordinated operation codenamed Viribus was led by Italy’s Carabinieri police and involved Interpol, the Joint Research Centre and the European Anti-Fraud Office OLAF.

Europol said the operation, co-led by Greek police, was the largest of its kind ever.

“Over the last 20 years, the worldwide trade in anabolic substances has increased significantly,” Europol said, citing athletes, gym fanatics and bodybuilders as users.

Breeders also use illegal hormones on animals, to fatten farm animals or enhance performance in horse races.

Police said they had shut down nine underground labs in European countries and seized almost 24 tonnes of raw steroid powder.

“We would like to congratulate all member states and other organisations that contributed to this successful operation,” said Gunter Younger, WADA’s head of intelligence and investigations.

“This is the sort of multi-party collaboration that produces real results and can make a significant impact on the availability of counterfeit and illegal drugs used by some athletes globally.”