Scientifically, Gifty understands that opioids work by flooding the brain with dopamine, which the brain craves. Eventually, the drugs stop providing euphoria and only offer relief from withdrawal. She attended a lecture Han gave on imaging of what it looks like in the brain when a person expects a reward. Afterwards, she asked what the brain looks like when someone does something very bad.
Just because Gifty understands from a physiological and scientific point of view how addiction works doesn’t mean that she truly understands addiction. Her research is an effort both to see if she can change the physiology of the addicted brain through optogenetics and to try to answer the unanswerable questions raised by the traumas of her childhood. From her question to Han, it’s clear that she feels more responsible for what happened to Nana than she’s previously let on—she’s been keeping the readers at arm’s length in much the same way she’s avoided intimacy with other people throughout the book.