Five sachets, believed to contain drugs, were found in prison cells yesterday in the second find there this week.
The items were discovered by sniffer dogs during a spot check by officials yesterday afternoon.
One inmate swallowed a suspicious substance, the Home Affairs Ministry said.
Random inspections at Corradino Correctional Facility became more frequent after Minister Manuel Mallia stepped up the fight against drugs in prison, declaring his ultimate aim was to clean up the place.
The substance found in the sachets was being analysed and further searches were carried out, the ministry said.
On Monday, two prisoners were caught red-handed during a raid when a suspicious substance was found in their cell.