Lembke begins this chapter with a more technical and scientific discussion in which she describes, in lay terms, how dopamine is transmitted within the brain. She discusses the various beliefs surrounding the extent of dopamine’s role in human motivation. Lembke points out that dopamine is released in the brain and doesn’t come from an external source such as a drug. She includes graphics to provide visual interpretation for her technical discussion of how dopamine relates to the pleasure-pain balance in the brain. Lembke points out that the centers for pain and pleasure are in the same place. She discusses tolerance—what it is and how it forms in relation to excessive dopamine release in the brain. Essentially, tolerance is the need to consume increasing quantities of a substance to achieve the desired effect. Eventually, tolerance reaches such a degree that no amount of consumption of the substance can create the original effect.

Lembke then discusses opioid addiction. Interestingly, the longer someone takes opioids, the less likely it is that the medicine will fulfill its intended purpose, which is to mitigate pain. In fact, Lembke argues that the inverse happens; the longer someone takes opioid medication, the more likely they are to experience pain.