Caffeine Calculator
How Does Caffeine Actually Work?
Caffeine is the world’s most widely consumed psychoactive substance. But unlike other stimulants that "add" energy, caffeine works by blocking the chemical that makes you feel tired.
Throughout the day, a chemical called Adenosine builds up in your brain. Adenosine binds to receptors, slowing down nerve activity and signaling "sleepiness."
The Molecular Trick: Caffeine looks almost exactly like Adenosine. When you drink coffee, the caffeine molecules float up to your brain and plug the Adenosine receptors. The Adenosine can't park, so you don't feel the signal to sleep.
The "Caffeine Crash" Explained
So, why do you feel exhausted at 2 PM? The caffeine wears off.
While the caffeine was blocking the receptors, your body didn't stop producing Adenosine. In fact, it created a backlog. Once the caffeine is metabolized and leaves the receptor, all that built-up Adenosine floods in at once.
Safety Limits: The 400mg Rule
The FDA sets the safe daily limit for healthy adults at 400 mg. This is not a random number; it is the threshold where negative side effects typically begin for the average population.
Exceeding 400mg often leads to:
- Insomnia and disrupted REM sleep
- Jitters, shaking hands, and anxiety
- Digestive issues and heartburn
- Heart palpitations (Tachycardia)
However, tolerance varies. A 250lb man who drinks coffee daily will react very differently than a 110lb woman trying coffee for the first time.
Hidden Sources of Caffeine
You know it's in coffee, but where else is it hiding?
| Product | Serving | Est. Caffeine |
|---|---|---|
| Pre-Workout Powder | 1 Scoop | 200 - 400 mg (Beware!) |
| Dark Chocolate | 1 Bar (1.5oz) | 30 mg |
| Excedrin (Pain Meds) | 2 Pills | 130 mg |
| Decaf Coffee | 8 oz Cup | 2 - 5 mg (Not zero!) |
Is Caffeine Dehydrating?
This is a persistent myth. While caffeine is a mild diuretic (makes you pee), the liquid in the coffee usually compensates for the fluid loss.
Studies show that regular coffee drinkers maintain hydration levels similar to water drinkers. However, pure energy drinks loaded with sugar and caffeine can be dehydrating if you don't drink water alongside them.
Can You Die from Caffeine?
Yes, but it is extremely difficult to do with coffee. The lethal dose is estimated to be around 10 grams (10,000 mg).
To reach this, you would need to drink about 75-100 cups of coffee in rapid succession. Your stomach would reject the liquid volume long before the toxicity killed you. However, Pure Caffeine Powder supplements are dangerous because a single teaspoon can contain 5,000 mg—half a lethal dose. Always measure powders carefully!