Chicago's largest jail, and the largest single use jail in America, is Cook County.
In 2023 it saw a spike in overdose deaths. The facility, which averages one or two overdose deaths a year, lost eight inmates that year to fatal seizures. Security footage shows prisoners spasming and collapsing.
Traditional drugs were usually brought into the jail in body cavities, so the jail had the same body scanners you find at airports to prevent that happening. However, a new way of drugs entering the prison was uncovered. Drugs were being mailed into the jail soaked in the paper of the pages of books and in letters.
The BBC's Quentin Sommerville joined corrections officers at Cook County as they prepared for an early morning raid on the jail's high security D block.
To understand the challenge that authorities face in tackling the problem the BBC interviewed a former inmate and dealer, who explained how synthetic drugs can be made in the US using household ingredients and how this could change the demand for drugs from outside of the country.