50 free Caffeine trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Caffeine is the most widely consumed psychoactive drug on Earth, legal almost everywhere and swallowed at a rate of 120,000 tonnes a year. This quiz covers the science: how it blocks adenosine to keep you awake, why plants make it as a pesticide, its half-life and what smoking, the pill and pregnancy do to it, the doses that are safe, the doses that are lethal, and the odd corners of medicine where it treats premature babies and boosts painkillers. It also covers the history and the products: Runge and Goethe's coffee beans in 1819, Emil Fischer's synthesis, the kings who banned coffee, the US government's 1911 seizure of Coca-Cola, Roselius and the seawater that invented decaf, Lipovitan, Krating Daeng and Red Bull, Monster and the energy shot, plus kola nuts, yerba mate, gyokuro tea and the Mormon reading of 'hot drinks'. It suits coffee drinkers, science quiz fans and anyone who has wondered whether the fourth cup is a good idea. Every answer was checked against Wikipedia's articles on caffeine, decaffeination, energy drinks and Red Bull, and each question shows its supporting sentence after you answer.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Caffeine keeps you awake mainly by blocking the receptors of which sleep-promoting molecule?
Adenosine
The molecule builds up in the brain the longer you stay awake; caffeine has a similar shape and sits in its receptors without switching them on.
Q 02To which chemical class of stimulants does caffeine belong?
Methylxanthines
Its cousins theophylline and theobromine, found in tea and chocolate, are also methylxanthines and are used to treat asthma.
Q 03Caffeine is chemically related to which components of DNA and RNA?
The bases adenine and guanine
It is a purine alkaloid, a bitter white crystalline solid.
Q 04What title does caffeine hold among the world's psychoactive substances?
The most widely consumed
Global consumption is estimated at 120,000 tonnes a year, and unlike almost every other psychoactive drug it is legal nearly everywhere.
Q 05Why do plants such as coffee and tea make caffeine in the first place?
As a natural pesticide against insects
It can paralyse and kill insects, and it leaches into the soil to stop rival seeds germinating near coffee seedlings.
Q 06Caffeine has been found to enhance the reward memory of which animals, encouraging them to return to a plant?
Honey bees
For dogs, cats, birds and spiders, by contrast, it is toxic, because they metabolise it poorly.
Q 07Roughly how many plant species are known to contain caffeine?
About thirty
Coffee seeds and tea leaves are the familiar ones, but there are others from South America and West Africa.
Q 08Which German chemist first isolated caffeine, in 1819, calling it 'Kaffebase'?
Friedlieb Ferdinand Runge
French chemists isolated it independently two years later, and Berzelius eventually acknowledged the German's priority.
Q 09Which famous writer handed a young chemist a box of coffee beans to analyse in 1819, leading to the discovery of caffeine?
Johann Wolfgang von Goethe
The chemist had impressed him by dilating a cat's pupils with belladonna extract; a few months later he had identified caffeine.
Q 10Which future 1902 Nobel laureate first achieved a total synthesis of caffeine in 1895?
Emil Fischer
He worked out its structural formula two years later; industrial caffeine has since been synthesised from urea and chloroacetic acid.
Q 11The word 'caffeine' first appeared in print in which language?
French, as caféine
Pelletier used it in an 1821 article, from café; the 'théine' isolated from tea in 1827 turned out in 1838 to be the same compound.
Q 12In 1911 the US government seized 40 barrels and 20 kegs of which product, alleging its caffeine was 'injurious to health'?
Coca-Cola syrup
The Supreme Court case was literally titled United States v. Forty Barrels and Twenty Kegs of Coca-Cola, and the company won.
Q 13Which English king tried to ban coffee in 1676?
Charles II
Frederick II of Prussia banned it in 1777, and Sweden outlawed it several times between 1756 and 1823.
Q 21Regular caffeine consumption may reduce the risk of which neurological condition?
Parkinson's
It may also slow the condition's progression; the evidence for a protective effect against Alzheimer's is inconclusive.
Q 22Adding 100-130 mg of caffeine to common painkillers such as paracetamol does what?
More people get pain relief
Caffeine has been found to raise the potency of some over-the-counter analgesics by about 40%.
Q 23Which of these was caffeine formerly used as a second-line treatment for?
ADHD
It works better than placebo but worse than methylphenidate; people with the condition drink more caffeine, perhaps self-medicating.
Q 14How much caffeine per day does the European Food Safety Authority say raises no safety concerns for a healthy adult?
Up to 400 mg
That is roughly 5.7 mg per kilo of body weight; Health Canada uses the same 400 mg ceiling.
Q 15Roughly how much caffeine is in a 6-ounce cup of coffee?
50-175 mg
It depends on the bean, the roast and whether it is drip, percolated or espresso.
Q 16About how many ordinary cups of coffee would it take to reach a lethal dose of caffeine?
50-100
The fatal dose is around 150-200 mg per kilo of body weight, over 10 grams for an adult.
Q 17What quantity of pure powdered caffeine, sold as a supplement, can be lethal?
A tablespoonful
Several deaths have been linked to the powder, which is unregulated as a dietary supplement in the US.
Q 18What is the typical half-life of caffeine in a healthy adult?
3 to 7 hours
In newborns it can be 80 hours or more, and it roughly doubles in women taking oral contraceptives.
Q 19How does smoking tobacco affect the body's handling of caffeine?
Clearance speeds up by about 56%
Hydrocarbons in smoke induce the liver enzyme CYP1A2, which is why regular smokers tend to drink more coffee.
Q 20Caffeine citrate is on the WHO's list of essential medicines for treating which condition?
Apnea in premature babies
It also treats bronchopulmonary dysplasia in premature babies and can improve their weight gain and cut cerebral palsy risk.
Q 24Which amino acid found in tea has synergistic alerting effects when taken with caffeine?
L-theanine
A 2014 meta-analysis found the pair improved alertness, attention and task switching, mostly within the first hour.
Q 25Roughly what dose of caffeine per kilogram improves sprint, cycling and endurance performance?
About 5 mg/kg
It also raises basal metabolic rate and fat oxidation, and lowers perceived exertion during steady exercise.
Q 26Daily consumption of 1 to 1.5 grams of caffeine is associated with which condition?
Caffeinism
It combines dependency with nervousness, irritability, insomnia, headaches and palpitations.
Q 27Which of these is a recognised symptom of caffeine withdrawal?
Headache
Sleepiness, irritability, flu-like symptoms and trouble concentrating are the others; symptoms rarely last more than a day.
Q 28As of 2021, how does the World Health Organization classify caffeine?
Not an addictive substance
The DSM-5 lists 'caffeine-use disorder' only as a condition for further study, though ICD-11 recognises caffeine dependence.
Q 29Which US regulator classifies caffeine as 'generally recognized as safe'?
The Food and Drug Administration
It considers drinks with under 0.02% caffeine safe, while pure caffeine powder remains unregulated as a supplement.
Q 30Which merchant invented the first commercially successful decaffeination process in 1903, after seawater soaked a shipment of beans?
Ludwig Roselius
His original process used benzene, now known to be a carcinogen, so other solvents replaced it.