https://www.sun-sentinel.com/news/crime/fl-ne-fugitive-roy-k...

Someone was mailing drugs into federal prisons, disguising papers soaked in MDMA (commonly known as ecstasy), fentanyl, synthetic marijuana and Suboxone, an opioid dependence treatment, as confidential legal communication in order to sneak them past guards.

https://www.npr.org/2021/07/15/1015447281/overdose-deaths-st...

Friends and family can tuck strips of paper soaked with drugs into mail or books, and if they get past the mail room, people in prison can eat them, or roll them up and smoke them.

https://bangordailynews.com/2020/06/25/news/state/3-maine-wo...

Three Maine women have been accused of being associates to a New York City street gang called the Bullies that allegedly used vehicles with hidden compartments and comic book pages soaked in narcotics as part of their multi-state distribution of cocaine, heroin, guns and money between Maine and New York for 3 ½ years.

Found on first page of:

https://www.google.com/search?q=heroin+soaked+book