Notes
This book gives general information about an everyday habit. It isn't medical advice, and it's no substitute for a doctor or pharmacist who knows your case. The NHS guidance and figures I mention are for England as I found them in September 2026.
I've kept sources out of the chapters where I could so they read easily. Here they are by chapter, with the limits I'm aware of. Unless I say otherwise, I read the published summary of each paper and not the full text. I checked each paper for a retraction or correction notice in September 2026. Poole and colleagues has a published correction, which I haven't read. Where a chapter isn't listed, it rests on my own reasoning. That includes chapters 1, 2, 13, 14, 17, 18, 19 and 22. The Tuesday, the paragraph, the meeting at four, the drive home and everything else in the running example are invented.
Before you start. The pregnancy limit of 200 milligrams a day is from the NHS page "Foods to avoid in pregnancy", which also lists the caffeine content of common drinks used in chapter 11. The advice about tiredness, snoring and low mood is general and the NHS pages on sleep apnoea and depression describe the symptoms.
Chapter 3. Rogers, Hohoff, Heatherley, Mullings, Maxfield, Evershed, Deckert and Nutt, "Association of the anxiogenic and alerting effects of caffeine with ADORA2A and ADORA1 polymorphisms and habitual level of caffeine consumption", Neuropsychopharmacology 35, 2010, pages 1973 to 1983. One hundred and sixty-two non-or-low and 217 medium-or-high consumers, 16 hours' abstinence, 100 then 150 milligrams or placebo. The study's main purpose was genetic, and the alertness finding is from its secondary results. The sentence about no net benefit is close to the authors' own wording. James and Rogers, "Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation", Psychopharmacology 182, 2005, pages 1 to 8. I couldn't obtain a summary and have relied on the title, as the chapter says. The comparison with the person on the train is mine.
Chapter 4. Landolt, Werth, Borbély and Dijk, "Caffeine intake (200 mg) in the morning affects human sleep and EEG power spectra at night", Brain Research 675, 1995, pages 67 to 74. Nine healthy men. The description of adenosine and caffeine is from general knowledge of the pharmacology, and the Landolt abstract refers to adenosine's role. The account of the pick-up as a muffled message and a loan is mine.
Chapter 5. Rogers, Heatherley, Mullings and Smith, "Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance", Psychopharmacology 226, 2013, pages 229 to 240. Two hundred and twelve medium-to-high and 157 non-or-low consumers, overnight abstinence, 100 then 150 milligrams or placebo, tested until mid-afternoon. The application to the meeting at four is mine.
Chapter 6. Rogers and colleagues 2013 as above, for the worsening of withdrawal effects into the afternoon. The early afternoon dip in alertness is general knowledge of circadian rhythms and I haven't cited a specific source. The division of the slump into two causes is my reading.
Chapter 7. Clark and Landolt, "Coffee, caffeine, and sleep: a systematic review of epidemiological studies and randomized controlled trials", Sleep Medicine Reviews 31, 2017, pages 70 to 78. The authors note that most studies were in male adults in Western countries. Drake, Roehrs, Shambroom and Roth, "Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed", Journal of Clinical Sleep Medicine 9, 2013, pages 1195 to 1200. Four hundred milligrams, measured at home by self-report and a portable monitor. The NHS insomnia page says not to drink tea or coffee for at least six hours before bed. That caffeine leaves the body slowly over several hours is general pharmacology, and Landolt's saliva measurement is the nearest cited evidence.
Chapter 8. Drake and colleagues as above, for the effects at bedtime and three hours before it. The claim that people feel the difference within a few nights is my observation.
Chapter 9. Juliano and Griffiths, "A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features", Psychopharmacology 176, 2004, pages 1 to 29. Fifty-seven experimental and nine survey studies. The 50 per cent headache figure and the 13 per cent figure for significant distress are from experimental studies.
Chapter 10. Poole, Kennedy, Roderick, Fallowfield, Hayes and Parkes, "Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes", BMJ 359, 2017, j5024. Observational associations, which the authors say need trials to establish cause. EFSA Panel on Dietetic Products, Nutrition and Allergies, "Scientific Opinion on the safety of caffeine", EFSA Journal 13, 2015, 4102. The point that none of this research is about timing or pattern is mine.
Chapter 11. Caffeine figures from the NHS page as above. The arithmetic for the Tuesday example is mine and uses the NHS figures. The observation that most drinkers have their last caffeine later than they think is mine.
Chapter 12. The tea and green tea figures are from the NHS page as above, and the adult figure of no concern is from the EFSA opinion cited under chapter 10. The arithmetic and the observation about tea's reputation are mine.
Chapter 15. Rogers and colleagues 2010 and 2013 as above, for the anxiety and jitteriness findings in low consumers and tolerance in regular ones.
Chapter 16. Clark and Landolt, and Rogers 2010, as above. Everything else is my reckoning.
Chapter 20. Gollwitzer and Sheeran, "Implementation intentions and goal achievement: a meta-analysis of effects and processes", Advances in Experimental Social Psychology 38, 2006, pages 69 to 119. The rule and its parts haven't been tested together, and what I say to expect is my expectation and not a finding.
Chapter 21. NHS pregnancy figure and EFSA as above. The EFSA opinion says the information available is insufficient to derive a safe intake for children and adolescents. Everything else in the chapter is my own suggestion.