How to read this book

A few notes to make the tour easier.

The safety rule, first

This book explains diseases and drugs in enough detail that it would be easy to mistake it for clinical guidance. It is not.

Never act on this book alone. Doses, thresholds, and drug choices in these pages are illustrative, chosen to explain a mechanism. Real prescribing depends on your kidney function, your other medicines, your pregnancy status, your age, and a dozen other things a book cannot know. Use the book to understand what your clinician is doing and to ask better questions. Do not use it to overrule them.

Two situations override everything else in this book: new, severe, or sudden symptoms (chest pain, one-sided weakness, difficulty breathing, sudden severe headache, confusion, a stiff neck with fever, thoughts of suicide) mean emergency care now, not reading. And anything that changes fast deserves a real examination, because speed is itself a diagnostic clue.

Every disease chapter has the same twelve sections

The order is fixed, so you can jump straight to the part you want:

1. What it is
2. The history
3. What actually goes wrong
4. What it does to the body
5. Is it deadly?
6. Is it contagious?
7. Who gets it
8. Treatment, and how it works
9. What treatment costs
10. What the person can do
11. Living with it
12. What's next

Then sources and notes, then a 👉 arrow to the next chapter.

The first seventeen chapters are foundations rather than diseases, so they do not follow that template. Chapters 1 to 7 build the body itself: the molecules, the cells, and each organ with what it does, how much reserve it has, what damages it, and what protects it. Chapters 8 to 11 cover what food, movement, sleep, stress, and time actually do inside you. Chapters 12 to 17 cover how disease, immunity, genes, drugs, and evidence work. The last two parts, on populations and on drug terminology, do not follow the template either.

Boxes and signs to watch for

Don't be confused: ... boxes untangle two things people routinely mix up, like type 1 and type 2 diabetes, a heart attack and cardiac arrest, or HIV and AIDS. Mixing these up is not a small error. It changes what you think the disease is.

In short: lines sit directly under most section headings and compress that section into one sentence, so you can skim a chapter and stop where it matters.

Bold marks a technical term the first time it is defined. Tables compare things that are genuinely comparable. A "👉" at the end of a chapter points to the next.

If a term or a drug name is unfamiliar

Two places to look. The glossary defines every term the book uses. Chapter 67 is a decoder: it explains why a drug's name ending tells you its class, how medical words are assembled from about forty Greek and Latin pieces, how to convert between the two systems of lab units, and what the frequency words on a package leaflet actually mean numerically. If you have ever wondered why GLP-1 is called GLP-1, that is where the answer is, alongside Chapter 66, which covers that drug class in full.

Four words this book uses precisely

In short: Acute means fast rather than severe, chronic means long-lasting rather than mild, and a risk factor is not a cause.

Ordinary conversation treats these as synonyms. Medicine does not, and the difference matters in almost every chapter.

Two more pairs are worth fixing in your head now, because they recur constantly:

• Sign vs symptom. A symptom is what the patient feels (pain, nausea). A sign is what someone else can measure (a fever, a murmur, a blood result). Many of the most dangerous diseases in this book, hypertension above all, have signs long before they have symptoms. That is exactly why they are dangerous.
• Incidence vs prevalence. Incidence is how many new cases appear in a period. Prevalence is how many people have it right now. A disease that is easy to catch and quick to resolve has high incidence and low prevalence. A disease that is hard to catch and impossible to cure, like HIV in the treatment era, can have falling incidence and rising prevalence at the same time. Headlines confuse these two constantly.

On the numbers in the tables

In short: Global figures are modelled estimates, relative risk is meaningless without the baseline, and survival statistics describe groups rather than individuals.

Every chapter carries numbers: how many people have the disease, how many die of it, how much a treatment reduces risk. Three cautions.

Global figures are estimates, not counts. Nobody counted 589 million people with diabetes. That number comes from surveys of samples, extrapolated with a model. It is the best available answer and it is not precise to the last million.

Relative risk is not absolute risk. "Doubles your risk" is meaningless without the starting number. Doubling a 1-in-10,000 risk is a rounding error. Doubling a 1-in-4 risk is a catastrophe. Chapter 17 explains how to read this properly, and every chapter afterwards tries to give absolute numbers.

Survival numbers describe groups, not you. A "five-year survival of 20 percent" is a property of a large population diagnosed years ago, under older treatments, across all ages and stages. It tells you about the disease. It does not tell any individual their future.

Read in any order

The chapters are grouped by body system, but each stands alone. If you came here for one disease, go straight to it; it will link back to whichever foundation chapter it needs. If you are reading start to finish, the foundation chapters will make every disease chapter shorter and clearer.

If you want the practical version first, go to Chapter 64, which is the operational summary: what to do, what to measure, what to have screened and when, what the warning signs are, and what to ignore.

Use the search box (or press S) to jump to any disease, drug, or term.

With that, we start with the thing all of this happens to. 👉