Hank Green: By now we've gotten to know each other, and you may have noticed that I'm kind of a high energy guy. I can be loud, I've been known to talk a little too fast, I get really excited about nerdy things.... And you're probably thinking to yourself, "Oh, that Hank --he must have to drink a bunch of Rock Star, coffee, Red Bull, diet coke, other coke, and coffee, and Rock Star, and coffee (I already did coffee) to keep himself so peppy all the time.

And you would be wrong about that. This machine does not require caffeine to operate.

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I have been known to have a coke every once in a while, but in general I tend to avoid the world's most popular psychoactive drug. This makes me something of an aberration in a world that is caffeine-crazy, and by "crazy" I mean that today, millions of you will pay more for 12 ounces of this [tea/coffee] than for a gallon of this [petrol], and I don't even wanna talk about what happens to my friends when they go a couple days without the caffeine. Holy anxious irritable headachey people! That stuff's powerful.

Despite all this the sweet-tasting things that we tend to put into caffeinated beverages, caffeine itself is a bitter, white, powdery alkaloid. So, caffeine does have taste, which is why caffeine-free coke and coke taste different.

The world consumes over 260 million pounds of caffeine every year, and while most of it is extracted either from coffee or tea, there's a bunch of different natural sources. These include two South [American] plants, yerba mate and guarana. The latter you probably have heard of as an additive in some energy drinks. And there's also something called the kola nut, which is native to western and central Africa, which a lot of people chew on for its stimulating properties, and once upon a time it was used as flavoring for the popular caffeinated beverages that still bear its name today.

But since you, my dear viewer, have an active, analytical, sciencey mind, you're wondering right now why is it so stimulating? How does it work?

Basically, it tricks your brain into thinking that you're not tired. Caffeine, known to chemists as 1,3,7-trimethylxanthine, is actually similar in structure to naturally-occurring molecules in our body called adenosines. Adenosine bonds to receptor cells in the brain, which in turn has a calming effect on the entire nervous system, and that makes you sleepy. What caffeine does is it blocks those receptors in the brain before adenosine can get in there and do its thing. Instead of calming the nerve cells, caffeine stimulates them, causing increases in the heart rate and the blood pressure, increasing alertness and delaying the onset of fatigue.

People who love their caffeine love that feeling of alertness, that artificial brain chemistry bond is creating. Caffeine peaks in your bloodstream about 30 minutes after you first take it in and then it has a half life in your body of about six hours, so six hours after you drink it you're feeling half the effects, which is why people have to keep drinking throughout the day in order to maintain the feeling of alertness that that initial cup gave them.

And this raises the question of whether or not caffeine is addictive, and it sort of is, but technically it isn't. Caffeine can cause some physical dependence, but going cold turkey isn't going to give you anything like the withdrawal symptoms of nicotine or cocaine. You'll have a headache, you'll be cranky, but you'll feel better in a day or two, I promise.

Caffeine may feel pretty addictive, but it's more of a dedicated habit. It doesn't meet the scientific definition of what an addictive substance is. Unlike cocaine, scientists say, caffeine doesn't "pose a threat to society", and it doesn't activate these brain reward circuits that are kind of the key to actual physical addictions.

But going back to this friend of mine who has, like, two liters of Mountain Dew a day, and he mixes it up with espresso shots, should I be worried about that guy actually overdosing on caffeine? And the answer, thankfully, is no. Doctors recommend that the average person keep his or her caffeine intake below 300 milligrams per day. That's roughly the amount of caffeine in two 12-ounce cups of coffee. By comparison, a Red Bull contains about 80 mg of caffeine, while pills like No-Doz contain 200 mg per pill.

But here's the deal: Depending on your weight, you would need to consume between 6 and 7 grams of caffeine per day, which would be really hard to do unless you were dedicated to the cause and had a jar full of caffeine.

So unless my friend can slam 50-100 cups of coffee in a day, which I don't think anyone's stomach could actually be big enough to handle, he'll be okay. So good news, we can all stop being so nervous and just relax a little bit.

Thank you for watching this episode of SciShow. I'm gonna have a coke now. Uh, if you wanna learn more about caffeine, there's links in the description. If you wanna ask questions or suggest topics, you can hook up with us on Facebook or Twitter or of course in the YouTube comments below.

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