More than 100 suspected ecstasy tablets and cannabis bush were seized after an anonymous tip off in Accrington.
Officers from the Springhill and Central Neighbourhood Policing Teams made the discovery after raiding two addresses on Spring Street and Elizabeth Street on Friday, January 6.
Two men aged 18 and 27 and two women aged 18 and 45 were interviewed by the police and were released pending further enquiries.
Sgt Craig Shaw said: “The tablets have all been sent off for forensic analysis and enquiries continue to find out who was responsible.
“I hope people are reassured that we do listen to their concerns and will take action.
“I urge anyone with information or concerns about drugs in their neighbourhood to contact us.”
Cannabis concerns can be reported to the police on 101 or the independent charity Crimestoppers anonymously on 0800 555 111 or on-line at Crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.