new york said it's because they make profound changes in the brain soon after you start using them. >> this is where you actually get to look at the brains? >> exactly. >> hurd collects brains, hundreds of them from opioid addicts who have overdose. it's grim work. is there anything that's different about the brain of someone who's an addict versus someone else's brain? >> it is not gross changes. it is how the cells communicate with each other that are changed. >> hurd showed me under the microscope. this is a healthy brain. lots of cells, lots of connections. >> beautiful, the branching, the communication is essential for every single thing we do. >> this is a brain on drugs. specifically, opioids. >> so one of the things you can see is that there's not that many networks. >> looks like a poorly populated neighborhood. >> exactly. >> this is what a brain disease