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Substances & Exposure · Article

Caffeine

Where it hides in OTC drugs, the adrenal burden of daily use, and the WHO classification you weren't told about.

Rev. Allie Johnson

Sanctified Healer · Monastic Medicine Practitioner

This article has 5 parts. Part 1 of 5: Article

The Most Normalized Drug in History

If a new substance were introduced today that caused adrenal exhaustion, disrupted sleep architecture, depleted essential minerals, created physical dependence within days, produced withdrawal symptoms recognized in the DSM-5, and was sold to children in flavored beverages. It would never be approved. It would be controlled, restricted, and studied with urgency.

Caffeine exists in a category of its own not because its biology is different, but because its cultural history precedes the regulatory framework that would have scrutinized it. We built civilization around it. Coffee shops were the original internet. The morning cup is identity. And so the question, what is this actually doing to us? has never been asked loudly enough.

Stephen Cherniske, M.S., asked it in 1998 with Caffeine Blues, one of the most thorough and unflinching examinations of caffeine's effects on human biochemistry ever written. What follows draws from that work and from the decades of sleep and neuroscience research that have followed it.

What Caffeine Actually Does

Caffeine does not create energy. This is the central misunderstanding. Caffeine is an adenosine receptor antagonist. It occupies the same receptor sites as adenosine without activating them, blocking the signal. Adenosine is the brain's fatigue-signaling molecule, produced continuously as a byproduct of neural activity. It accumulates across the waking day, building sleep pressure that drives you toward rest.

When caffeine blocks adenosine receptors, the fatigue signal is silenced, but the adenosine continues to accumulate. The debt is deferred, not cancelled. When caffeine's effects wear off (typically 5–7 hours, though genetic variation extends this to 10–12 hours in slow metabolizers), the previously blocked receptors become available and the accumulated adenosine floods them simultaneously. That is the crash.

Caffeine doesn't give you energy. It borrows against the fatigue you've already earned, defers the debt, and delivers it with interest when the loan comes due.

Caffeine also triggers the adrenal glands to release cortisol and adrenaline. The brain and adrenal glands cannot distinguish between a bear in the road and a cup of coffee, the identical hormonal cascade fires. This is the full fight-or-flight response, activated by every single dose. With daily use, this creates a continuous background state of physiological stress that the body adapts to but never fully resolves.

After stopping caffeine, the adrenal system takes roughly 3–6 weeks to recalibrate. During that window, particularly in the first three weeks, fatigue often worsens before it improves, because the adrenals have been chronically outsourcing their cortisol production to an external substance and need time to resume doing it themselves. This is why people who quit feel worse before they feel better, and why "I tried quitting and felt terrible" is not evidence that caffeine is necessary.

The Side Effects: What It's Actually Doing

These effects are dose-dependent, cumulative, and individual: influenced heavily by your CYP1A2 genetic status, your adrenal health, your current nutrient levels, and how long you've been using caffeine. Many people are living with several of these simultaneously and attributing them to aging, stress, or "just how they are."

  • Adrenal exhaustion : chronic stimulation of the adrenal glands trains the HPA axis to outsource its cortisol output to caffeine. Over time, the body's natural morning cortisol peak diminishes and you feel you cannot function without chemical help. This is not laziness. It is a physiological adaptation.
  • Cortisol awakening response disruption : the body has a built-in cortisol peak 30–45 minutes after waking that should naturally produce alertness without any substance. Coffee consumed immediately on waking competes with and suppresses this peak, wiring you to need it.
  • Sleep architecture disruption : caffeine reduces slow-wave (deep) sleep by approximately 20% even when it doesn't prevent falling asleep. It also suppresses early-morning REM. A 2pm coffee leaves active caffeine circulating past midnight for slow metabolizers. Years of this costs significant restorative sleep depth.
  • Anxiety and nervous system dysregulation : caffeine elevates adrenaline and cortisol; in people already running on stress hormones, this tips into palpitations, irritability, racing thoughts, and a low-grade ambient anxiety that feels like personality rather than pharmacology.
  • Magnesium depletion : caffeine is a diuretic that increases urinary excretion of magnesium, a cofactor in over 300 enzymatic reactions including ATP synthesis, the cell's own energy currency. Chronic caffeine users commonly become magnesium depleted, making the fatigue caffeine is compensating for progressively worse.
  • Iron absorption interference : caffeine consumed within an hour of meals significantly reduces iron absorption. Iron deficiency is one of the most common undiagnosed causes of fatigue, particularly in menstruating women. Caffeine both masks and perpetuates the deficiency.
  • B vitamin depletion : caffeine increases urinary B vitamin excretion and drives elevated demand for B5 (pantothenic acid) and B6 through the adrenal stress pathway; B5 is required for cortisol synthesis; the vitamins the body uses to produce energy are being depleted by the substance used to compensate for low energy.
  • Vitamin C depletion : the adrenal glands have the highest concentration of Vitamin C of any tissue in the body; every fight-or-flight activation burns through adrenal Vitamin C stores; chronic caffeine use is one of the most significant and underrecognized drivers of Vitamin C depletion; the adrenal cortex requires Vitamin C to synthesize cortisol, which means every dose of caffeine both depletes Vitamin C and demands more of it simultaneously.
  • Calcium depletion : caffeine increases urinary calcium excretion; this loss compounds with magnesium loss, since both minerals are required for bone integrity, muscle contraction, and nerve signaling; the long-term clinical consequence is reduced bone mineral density, most visible in postmenopausal women or anyone with low baseline calcium intake.
  • Zinc depletion : caffeine increases urinary zinc excretion; zinc is essential for immune function, testosterone production, wound healing, and over 100 enzymatic reactions; chronic caffeine users losing zinc continuously alongside magnesium are running a quiet mineral deficit that shows up as slow healing, lowered immunity, and hormonal disruption.
  • Copper depletion : caffeine use has been associated with altered copper status; copper is required for iron metabolism, connective tissue integrity, and neurological function; it exists in a tight balance with zinc. Both are being depleted, which compounds the disruption to the enzymatic systems that depend on them.
  • Blood sugar dysregulation : caffeine-driven cortisol and adrenaline release triggers hepatic glucose release, temporarily raising blood sugar. Over time this contributes to insulin resistance. The post-lunch energy crash many people treat with a second or third coffee is often a blood sugar drop. A symptom caffeine is being used to manage without addressing the cause.
  • Digestive disruption : caffeine stimulates gastric acid secretion and accelerates colonic motility (why it "gets you going"). Over time, reliance on caffeine for normal bowel function is common, along with increased acid reflux, gastritis, and disruption of the gut's natural rhythm.
  • Hormonal interference : elevated cortisol from chronic caffeine use suppresses thyroid function (via TSH suppression), disrupts sex hormone production (the cortisol-progesterone steal), and worsens conditions driven by hormonal imbalance including PMS, perimenopause symptoms, and thyroid underfunction.
  • Cardiovascular effects in slow metabolizers , individuals with the slow CYP1A2 variant have significantly longer caffeine half-lives and demonstrated increased risk of heart attack at higher caffeine intakes (Cornelis et al., JAMA 2006). Elevated blood pressure from chronic caffeine use is well-established across metabolizer types.
  • Tolerance and dependence : chronic caffeine use causes the brain to upregulate adenosine receptors to compensate for the blockade. More receptors means more caffeine needed for the same effect. Eventually the user is not drinking coffee to feel good. They are drinking it to feel normal.
  • Withdrawal (DSM-5 recognized) : headache (from cerebral vasodilation as vessels that were chronically constricted suddenly dilate), marked fatigue, irritability, depressed mood, difficulty concentrating, flu-like muscle aches; onset 12–24 hours after last dose, peaks at 20–48 hours, typically resolves within 9 days.
  • Reduced brain functional connectivity : a 2021 study in Molecular Psychiatry found that regular high caffeine consumption negatively impacts brain functional connectivity in the somatosensory and limbic systems, the regions governing attention, alertness, motor control, learning, memory, and emotional regulation. These are the same systems activated in fight-or-flight. Reduced connectivity is not a subjective feeling. It is a measurable structural change.
  • Brain dehydration : approximately 80% of brain mass is water. Caffeine's diuretic effect combined with its disruption of intracellular hydration can contribute to reduced brain water content, impairing focus, memory, and mood: independently of any direct neurochemical effect.

What Caffeine Takes From You: Per Dose, Every Day

Caffeine depletes or impairs absorption of the following nutrients through urinary excretion, adrenal demand, and gut chelation. These losses are not offset by the one cup. They compound across years.

Magnesium

ATP synthesis, 300+ enzymes, sleep and muscle function

Vitamin C

Adrenal glands burn Vitamin C with every fight-or-flight activation, the highest concentration of any tissue

Increased urinary excretion; cumulative bone density loss over years

B Vitamins (B1, B5, B6)

Urinary loss + elevated adrenal demand; B5 required for cortisol synthesis

Immune function, hormone production, 100+ enzymatic reactions

Iron metabolism, connective tissue, neurological function; depleted alongside zinc

Iron absorption is also impaired, not depleted directly, but the tannins in coffee block 60–90% of non-heme iron absorption when consumed within an hour of food.

Regular coffee consumption is associated with smaller brain volume, higher likelihood of dementia, and higher likelihood of stroke.

The large-scale study investigated the effects of habitual coffee drinking on total brain volume using data from over 17,000 participants. Results showed a dose-dependent relationship between coffee intake and decreased brain volume, with those drinking more than 6 cups per day showing the most pronounced effect, along with significantly higher rates of dementia and stroke risk.

Caffeine reduces cerebral oxygenation within minutes

MRI studies measuring cerebral blood oxygenation show a rapid, measurable drop in brain oxygen levels following caffeine ingestion, regardless of whether the person "feels" any effect.

Where Caffeine Hides: Beyond the Coffee Cup

Caffeine is an alkaloid occurring naturally in over 60 plant species: coffee beans, tea leaves, cocoa, kola nuts, guarana berries, yerba maté, guayusa, and yaupon holly. It is also added to hundreds of commercial products including sodas, energy drinks, kombucha, candies, and both over-the-counter and prescription medications, often without any warning, and sometimes without clear labeling.

People who believe they have reduced or eliminated caffeine are often still consuming it through medications they take daily. People tracking symptoms of anxiety, palpitations, insomnia, or headaches rarely think to look at their drug cabinet.

Over-the-Counter Drugs Containing Caffeine

Note: A typical cup of coffee contains 80–150mg caffeine depending on brew strength. NoDoz and Vivarin deliver more caffeine per tablet than most cups of coffee.

Prescription Drugs Containing Caffeine

Caffeine is used in some prescription pain and migraine formulations as a "co-analgesic". It enhances the absorption of pain medications and constricts cerebral blood vessels (useful for certain headache types). Patients are rarely told their prescription contains caffeine, meaning they may be consuming 40–100mg of caffeine per dose without knowing.

Caffeine Content in Common Beverages & Foods

For a more complete database of caffeine content in drinks, candy, and other sources: caffeineinformer.com/the-caffeine-database

Cancer Classification: What It Actually Says Now

Coffee is often described online as a "Class 2B carcinogen." That is out of date, and this page previously said it too. Coffee drinking was classified Group 2B, possibly carcinogenic, by the International Agency for Research on Cancer in 1991. IARC re-evaluated it in June 2016 and withdrew that classification. In IARC Monographs Volume 116, summarised in The Lancet Oncology on 15 June 2016, a working group of 23 scientists reviewed more than 1000 human and animal studies and concluded there was "inadequate evidence for the carcinogenicity of coffee drinking overall." Coffee drinking was moved to Group 3, not classifiable. The same review found coffee had no carcinogenic effect for cancers of the pancreas, breast and prostate, and that reduced risks were seen for cancers of the liver and uterine endometrium. What that same evaluation did classify is more interesting, and almost nobody repeats it. Drinking very hot beverages, defined as above 65°C, was classified Group 2A, probably carcinogenic, for cancer of the oesophagus. In the agency's own words, "it is the temperature, rather than the drinks themselves, that appears to be responsible." So the honest position is the reverse of the popular one. The evidence does not support calling coffee a carcinogen. It supports not drinking it scalding hot. Separately, acrylamide does form when beans are roasted, and that is a real compound worth understanding on its own terms rather than through a classification that no longer exists. And the California question, because the signs are still up. California has not required a Proposition 65 cancer warning on coffee since 1 October 2019, when Title 27 CCR section 25704 took effect, declaring that exposures to listed chemicals "created by and inherent in the processes of roasting coffee beans or brewing coffee do not pose a significant risk of cancer." It was upheld on appeal in Council for Education and Research on Toxics v. Starbucks Corp. (2022) 84 Cal.App.5th 879. Acrylamide itself is still on the Proposition 65 list. What changed is not the listing, it is the warning duty for this one exposure. If you still see a warning in a coffee shop, it is most likely old signage, a warning a business posted voluntarily during the litigation and never took down, or a sign about something else in the building such as the car park. The appellate court went further and said such warnings were "unnecessary and misleading regarding the risk of cancer from coffee."

Decaf Is Not the Answer

Switching to decaf is one of the most common moves people make when they want to reduce their caffeine intake, and it solves far less than it appears to. Three problems remain that are rarely disclosed:

1. It still contains caffeine.

Decaffeinated coffee retains 10–30% of the original caffeine content. The 2–25mg range in the table above is the industry average, some decaf cups test at the higher end consistently. For someone using "decaf" to manage anxiety, insomnia, palpitations, or adrenal fatigue, this residual load is not trivial, particularly across multiple cups per day.

2. The decaffeination process adds a chemical burden.

The majority of commercially sold decaf coffee is processed using one of two solvents: methylene chloride (dichloromethane) or ethyl acetate. Methylene chloride is a known carcinogen and neurotoxin, the FDA permits trace residues in finished decaf at levels the agency considers "safe," but the compound is classified as a probable human carcinogen by the EPA and is on California's Proposition 65 list. The solvent binds to the coffee oils and is not fully removed by the rinsing and drying stages. The only decaffeination method that uses no chemical solvents is the Swiss Water Process, it uses water and activated charcoal to filter caffeine. Very few mass-market brands use it.

3. Coffee itself carries a mycotoxin burden that decaffeination does not remove.

Coffee is one of the most heavily mold-contaminated food crops in commercial agriculture. Ochratoxin A, a nephrotoxic and immunosuppressive mycotoxin produced by Aspergillus and Penicillium mold species, is found in a significant percentage of commercial coffee samples globally. The mold colonizes green beans during storage and transport before roasting; roasting reduces but does not eliminate the toxin. Ochratoxin A accumulates in the kidneys, is classified as a possible human carcinogen (IARC Group 2B), and is particularly problematic for people with pre-existing liver or kidney burden. Decaf coffee carries the same ochratoxin risk as regular coffee. Caffeine removal does not affect mycotoxin content.

If the goal is reducing caffeine without eliminating coffee: look for Swiss Water Process decaf from a single-origin, third-party mold-tested roaster. If the goal is reducing overall coffee burden, the question is whether the ritual is worth the trade-off, or what the body would do without it.

An open question worth asking: Research in building biology has documented that non-native electromagnetic fields (WiFi routers, smart meters, and cellular signals) trigger a measurable stress response in fungi, increasing mycotoxin production as a survival mechanism. If this is occurring in the walls of mold-affected homes, the same electromagnetic environment exists in every kitchen where a coffee bag sits next to a router, where ground coffee is stored in a WiFi-saturated cabinet for weeks, or where a pantry full of other mold-prone foods (nuts, grains, dried fruit, corn products, aged cheese) is bathed in the same continuous RF exposure. The primary ochratoxin burden in coffee is agricultural and pre-roast. Whether ambient WiFi in the home accelerates further mycotoxin activity in already-colonized or spore-exposed foods is not yet established in the published literature, but the mechanism is documented, the exposure is universal, and the question has not been asked. It should be.

What It's Masking

If you need caffeine to feel awake, to think clearly, to have motivation, to go to the bathroom, what physiological state would exist without it? Caffeine is not creating function. It is masking dysfunction.

  • Iron deficiency : test serum ferritin (not just hemoglobin); commonly low in menstruating women; caffeine both masks the fatigue and worsens the absorption
  • Subclinical hypothyroidism : fatigue, brain fog, cold intolerance, mood issues; test full thyroid panel including free T3, free T4, reverse T3, and antibodies: not just TSH
  • HPA axis burnout : adrenal dysregulation from chronic stress, poor sleep, or blood sugar instability; caffeine forces output from a system already running on fumes
  • Poor sleep quality : the most common; if sleep were restoring properly, adenosine would be cleared each night and morning alertness would be natural
  • Blood sugar instability : the afternoon crash is often blood sugar, not simply adenosine; addressing diet removes the demand for a second or third coffee

Next: Children & Schools →

Caffeine and the Developing Brain

Energy drinks, school vending machines, hidden sources, deaths, and the question nobody is asking: why does a child over 12 have a caffeine limit at all?

Also: Pregnancy →

Caffeine in Pregnancy

How the guidance shifted, what the fetal harm data shows, and why the 200mg guideline is an accommodation, not a safety finding.

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