"I know my body better than a leaflet does"

You do, in the sense that counts. You know when you're low, when your chest is tight, when the tablet makes you sick, when your sleep has changed. No leaflet knows any of that, and a prescriber who dismisses it is doing a bad job. The book has spent several chapters saying that these feelings are information and should be taken to the conversation, not thrown away.

What you don't know from the inside is your blood pressure, your cholesterol, or your thyroid hormone level, because they don't feel like anything. That's not a failure of self-knowledge. It's just what those things are. The person who trusts their body to tell them whether the silent ones are needed is asking their body a question it has no way of answering, and the silence they get back isn't a no.

So the honest version of this belief is to know your body with instruments where instruments are the only way. The NHS blood pressure page describes home monitors and says a GP may ask you to use one over a few days. Pharmacies do free checks for the over-forties. Levothyroxine comes with regular blood tests, the NHS says, to check you're on the right dose, and being on the wrong dose has side effects of its own. A peak flow meter tells you how your airways are doing before your chest does. These are the readouts the missed-week experiment in chapter 5 never had.

There's a nice thing that happens when you have a number. The tablet stops being an act of faith. You take it, the reading comes down, you stop, over weeks it goes back up, and now the medicine has done something you can see. That's the feeling-fine test replaced with a test that works, and it converts a lot of people who couldn't be argued into a tablet by any leaflet.