Thirteen Preston properties were raided by officers from Preston police on Wednesday morning.
AdvertisementLancashire Police said eight people had been arrested on drug related offences.
The raids were part of Operation Nemesis which has seen more than 20 people charged with drugs offences across the city.
Police acted on information reported anonymously from the public about suspicions of drug dealing in the city.
No further information on those arrested has been released by the police.