Three men and a woman were arrested in a police drug raid in Pietà on Thursday.
The police said on Friday they raided a residence in Mountbatten Street, where illegal substances, including cocaine and heroin, were allegedly being consumed.
During the raid the police found items related to the sale of cocaine and heroin as well as cash.
They said the people arrested, aged between 29 and 48, attempted to destroy evidence by throwing drug sachets in acid. The men hailed from Attard, Pietà and Tarxien while the woman was from Dingli.
An inquiry is being held.