I listened to a really interesting Ezra Klein podcast about chronic pain treatment and the importance of taking a whole body approach. The guest’s main point is that pain originates with an injury or illness, but the patient’s experience of it can be influenced by their day to day life, mental health, supportive care, and levels of stress. I wish I could express it better, because when I write this out it sounds like I’m saying “it’s all in your head!”, but that is definitely not what she was saying. But it would explain someone having reduced relief from pain medication when they don’t have a biochemical reason to do so.

TLDR Pain is a complex sensation and what people experience is hard to understand.