Last weekend, members of the drugs squad under Det Sgt Alan Cullen found heroin worth almost €9,000 in the house at Briarfield, Castletroy.
A woman in her 30s was arrested in the house and detained at Henry Street Garda Station. She was released without charge and a file is being prepared for the DPP.
In the latest raid on the house, heroin with a street value of about €70,000 was discovered.
A man aged 39 who was arrested in the house this time is still being held under the Drug Trafficking Act.
Meanwhile, on Friday gardaí discovered cocaine worth €50,000 in a house in Drombana on the outskirts of the city. A man was also arrested and questioned at Roxboro Road Garda Station.
Supt Frank O’Brien said more raids are now targeting gangs in the city, who supply wide areas of the mid-west and Kerry.
The superintendent, who set up a special drugs unit at Roxboro Road station two years ago, revealed he has now set up a similar unit at Mayorstone Station.
Both units work with the divisional drugs squad based in Henry Street.
The new unit in Mayorstone consists of a sergeant and four gardaí, who underwent special training in countering the movement and sale of drugs.