Caffeine works by blocking adenosine, the brain chemical that builds up through your day and makes you feel tired. Block that signal and you feel more awake, more alert and better able to keep going. It reaches your bloodstream fast, so most people feel it within 5 to 30 minutes, and the average adult clears half of it in about five hours. Everything after that comes down to three things: how much you take, when you take it and how sensitive you are.
TL;DR
- Caffeine does not hand you energy. It blocks the signal that makes you feel tired, so the lift is real and it is temporary.
- Timing matters. A 100 mg dose close to bedtime can change how long and how well some adults sleep.
- Short term, a moderate dose sharpens alertness. More than you are used to brings restlessness, jitters, an upset stomach and a harder time winding down.
- Long term, the change most people notice is tolerance. The same dose does less, and skipping it feels worse.
- 100 mg is about one 250 ml cup of instant coffee, and it is what one 10 g scoop of Hoola carries.
- Health authorities put the everyday reference point at 400 mg a day for most healthy adults, counted across every source.
What does caffeine actually do in your body?
Caffeine blocks adenosine, a chemical that builds up in the brain while you are awake and turns up the feeling of being tired. The two molecules are similar enough that caffeine fits the same receptors, so adenosine arrives and finds its spot taken. The tiredness signal never lands. The alertness you feel comes from a quieter tiredness signal, not extra fuel in the tank, and it runs mainly through one receptor subtype called A2a.
Caffeine is not fussy about geography. It crosses into the brain easily and blocks adenosine receptors throughout the body, which is why one dose can feel like focus in your head and a churning stomach at the same time.
Almost all of a swallowed dose reaches your bloodstream, and food in the stomach slows absorption a little, so the lift lands slightly later after a meal. A 2025 review of the research puts it plainly: caffeine reduces fatigue and sharpens alertness. Most people feel the effects inside half an hour.
How long does caffeine last?
Plan on about five hours for half of it. That is the average half-life in adults, and the rest keeps clearing after that. Run the numbers on a 100 mg serve and the tail is easy to picture: roughly 50 mg is still in your system five hours later, about 25 mg at ten hours and about 12 mg at fifteen hours.
Five hours is an average, not a promise. Smoking cuts the half-life by up to half, so a smoker clears caffeine up to twice as fast as a non-smoker. Sensitivity runs the other way. Caffeine affects some people far more than others, and small amounts can leave one person restless and awake while another notices nothing.
How long you feel caffeine and how long caffeine lasts are two different clocks. One Australian fact sheet puts the noticeable effects at up to six hours, and notes that for some people they can run up to 12 hours. You can stop feeling wired well before your body has finished with the dose.
Sleep is where the tail matters most. A 100 mg dose taken close to bedtime can change how long and how well some adults sleep, even when the buzz has worn off.
What does caffeine do in the short term?
The short-term story is alertness first, then a set of effects that show up when the dose outruns your tolerance. At a moderate dose, caffeine raises alertness and attention, and reviews of the research describe faster reaction times and better concentration.
Take in more than you are used to and the same mechanism turns loud. Adenosine stays blocked, the stimulant side keeps building, and the effects are hard to miss: restlessness, excitability, jittery hands, an upset stomach, a headache and more trips to the bathroom.
There is a rebound as well. A review of caffeinated energy drinks found that people felt more alert and in a better mood for a few hours, then more tired than usual the following day.
If the jittery part sounds familiar, why caffeine gives you the jitters explains what is happening and how to take the edge off.
What changes with long-term caffeine use?
Regular use changes your baseline, and the first change is tolerance. Drink caffeine daily and your body adjusts, so the same cup does less and the dose creeps up to keep the effect.
Dependence is the second change. Caffeine is habit-forming, and a 2025 review of the evidence notes that while a single dose improves alertness, prolonged use can lead to dependency and diminishing returns.
Stop suddenly after a long habit and the body notices. Withdrawal usually starts within 12 to 24 hours, peaks in the first day or two and eases over about a week. Headache, tiredness, crankiness and trouble focusing are the usual shape of it. Caffeine withdrawal symptoms are worth understanding before you cut back, because the timeline is predictable and stepping down beats stopping cold.
The heavy-use picture is where the long-term effects concentrate. The Alcohol and Drug Foundation points at regular use of more than about four cups of coffee a day, and describes the pattern that builds there: broken sleep, irritability, headaches and a shaky, over-stimulated edge. What the research is still thin on is the decades-long view, and a 2025 review notes that studies tracking cumulative outcomes over time remain limited.
What does 100 mg of caffeine look like in real drinks?
100 mg is roughly one cup of instant coffee, one caffeine tablet, or one scoop of Hoola. Caffeine content varies more than most people expect, and the spread across everyday caffeine sources is why labels matter.
| Drink or product | Typical caffeine |
|---|---|
| Instant coffee, 250 ml cup | 80 mg |
| Espresso, 50 ml cup | 145 mg |
| Black tea, 220 ml cup | 50 mg |
| Cola, 375 ml can | 36.4 mg |
| Energy drink, 250 ml | 80 mg |
| Caffeine tablet | 100 mg |
The drink figures come from the Alcohol and Drug Foundation's caffeine fact sheet, with the tablet figure from Victoria's Better Health Channel. A takeaway coffee is the least predictable item on the list, because the number moves with the coffee type and the cup size.
Hoola sits at the same mark as the tablet. We carry caffeine at 10 mg per gram of powder, so one 10 g scoop is 100 mg. That figure is published with the other 26 actives on the Australian Register of Therapeutic Goods, where anyone can check it.
How does a 100 mg daily serve fit into a real day?
One scoop of Hoola is 100 mg, taken once a day. There is no half serve and no double serve, so the number stays fixed and easy to count.
The rest of your day is where the total moves. Add a 250 ml instant coffee and you are at about 180 mg. Add a second and you are at about 260 mg, which sits under the 400 mg a day that health authorities treat as the reference point for most healthy adults.
Timing matters as much as the total. We built the serve for the morning or early afternoon, which keeps the tail of the dose clear of the hours where caffeine can affect sleep. For context, the average Australian intake is about 210 mg a day for a 70 kg adult, or roughly two and a half 250 ml cups of instant coffee. A 100 mg serve alongside a coffee or two is an ordinary day rather than a heavy one.
Hoola is listed on the Australian Register of Therapeutic Goods, AUST L 508472, with every active and its quantity on the public record. Caffeine sits in the formula alongside Alpinia galanga (enXtra), and the full breakdown is on our ingredients and benefits page. You can see the full formula and the pouch sizes when you are ready.
Who tends to keep an eye on their total caffeine?
Four groups watch the total more closely: people who feel caffeine strongly, people who protect their sleep, athletes running under code rules, and anyone whose day stacks several sources without noticing.
Sensitivity sits at the centre of it. Caffeine affects some people far more than others, and even small amounts can leave some people restless or awake at night. Sleep is the next reason. Anyone protective of their nights tends to watch the timing of the last dose rather than the daily total, because a late 100 mg serve can land in the hours that matter most.
Athletes watch it for a different reason. Caffeine is not on the World Anti-Doping Agency's prohibited list, and the Australian Institute of Sport lists it as a Group A substance, supported for use in specific situations and permitted for some athletes under best-practice protocols, so the rules move with the sport.
The easiest group to join is the last one. Coffee, tea, cola and chocolate all count toward the same daily total, and in Australia the average intake is about 210 mg a day for a 70 kg adult, which is roughly two and a half cups of instant coffee before any supplement is added. Keep two numbers in your head, 100 mg for the scoop and around 80 mg for an instant coffee, and the running total stays visible without an app.
Frequently asked questions
How long does caffeine stay in your system?
Longer than the buzz suggests. The average adult clears half of a dose in about five hours. The rest keeps clearing for hours after that, so an afternoon coffee can still be in play at bedtime.
How much caffeine is too much?
For most healthy adults, health authorities put the everyday reference point at 400 mg a day across all sources combined, which is roughly five 250 ml cups of instant coffee. Regular heavy use, more than about four cups of coffee a day, is where the effects worth managing show up.
What are the signs of too much caffeine?
Restlessness and jittery hands come first, often with an upset stomach, a headache and more frequent trips to the bathroom.
Does the time of day matter?
Yes, more than most people expect. A late 100 mg serve can change sleep for some adults, and people who rarely use caffeine tend to notice it most.
Do you build a tolerance to caffeine?
Yes. Regular use teaches the body to expect caffeine, so the same dose does less over time, and skipping it feels worse than it did before the habit. Stepping intake down gradually is easier on the system than stopping overnight.
Is caffeine good or bad for you?
It depends on the dose, the timing and how you respond to it. Most adults take caffeine daily, and up to 400 mg a day across all sources is the level health authorities describe as raising no concerns for healthy adults. The parts worth managing are the ones you can feel: your sleep, your jitters and your running total.
How much caffeine is in a serve of Hoola?
100 mg, from 10 mg of caffeine per gram of powder in a 10 g scoop. That is a little above a 250 ml cup of instant coffee and below a 50 ml espresso, and it is published with the other actives on the public register under AUST L 508472.
