Thousands of drug users in County Durham and Teesside are being warned they face being poisoned after batches of contaminated heroin were discovered.
The drug, which had been mixed with cement, was discovered during raids on 24 properties carried out by the Cleveland and Durham forces.
Nineteen people were arrested on suspicion of drug offences.
Det Supt Tom Stoppard of Cleveland Police said drug addiction brought misery to those affected.
He said: "The reality of how difficult and dangerous this whole business is and the misery it causes becomes apparent after raids like these.
"Some unfortunate people die because of their heroin use and the time has come for this to stop."
Det Supt Stoppard said there were 2,000 heroin addicts in Stockton and Middlesbrough alone and the rising price of crack cocaine meant addicts often used heroin as a cheaper alternative.