When evidence is used to prove guilt in a criminal case, that evidence needs to be valid. It's a basic tenet of the criminal justice system that prosecutors aren't supposed to fight simply to win, but to fight for justice. They're not supposed to cut corners on evidence, and if there is a problem with that evidence, they're required to tell the defense.
Sadly, when it comes to drug addiction, the focus is often on punishing the crime rather than helping victims who cannot escape. That is slowly changing in Tennessee though. Tennessee has implemented recovery court, which is an alternative to jail time for drug crimes. It focuses on rehabilitation and breaking the cycle of addiction. If you have been convicted of a drug crime, this may be an option for you