There has now been a total of eight drugs arrests in Derry since the weekend.
Officers found a number of suspected Ecstasy tablets during the arrest of a woman in Derry City Centre in the early hours of this morning.
The 33-year-old was detained after police were called to Market Street at about 2.30am. She was later released on bail pending further police enquiries.
Meanwhile, a 33-year-old man was arrested at Glendermott Road yesterday evening on suspicion of possessing a Class B drug. He was released on bail pending further enquiries.
And a 23-year-old man was arrested after herbal cannabis was seized when police stopped a car in Ballymagroarty this afternoon. He remains in custody.
Five other arrests for suspected drugs offences were made over the weekend.
Chief Inspector Tony Callaghan said the arrests and seizures underlined the determination of police to tackle drugs issues in the city.