Lembke begins Part 3 with an anecdote about Michael, a patient recovering from cocaine use who discovered cold-water immersion therapy as a way to keep his mood elevated once he quit the drug. Lembke then describes what cold-water immersion therapy is and how it affects dopamine levels. She points out that for most of human history, cold-water bathing was the norm. The author again includes the teeter-totter diagram, explaining how cold-water immersion therapy presses on the pain side, which inevitably increases a pleasure response as the brain seeks homeostasis. Essentially, it’s the inverse of how a drug like cocaine presses on the pleasure side, resulting in pain once the person comes down from the temporary high.

Lembke stays with the theme of this chapter as she explores “The Science of Hormesis” which studies how discomforting and even painful stimuli affect the brain. She discusses how response to discomfort moderates behavior in the natural world and then mentions a few other examples of how humans can intentionally perform activities meant to inflict discomfort. Intermittent fasting is one example. Lembke continues her examination of the idea of using pain to treat pain and highlights various scientific research, culminating in a section that discusses electroconvulsive shock therapy, which—surprisingly, to many—is still used today.