Tea drunk explained: what caffeine and L-theanine do to your mind

November 2, 2026

Tea drunk on a spring afternoon

I heard about tea energy (chaqi) and being tea drunk (chazui) not long after I discovered real loose leaf Chinese tea. I nodded along, but didn't really get it.

Then came an afternoon in a tea house with a few friends, two or three good teas, a pitcher going round while we caught up on everything and nothing. Nobody was counting the infusions.

We walked out into one of those fine spring days in Paris, with sparkling sun and a gentle breeze. And my head felt different. Clear, calm, focused. Full of energy, but not wired. Just good.

No buzz to chase, no crash waiting around the corner. That was the day I understood what people meant. Tea gets you high, differently.

So what is actually going on?

If tea were just a weaker coffee, it would wake me up and that's it. But this was something else. Energy and calm at the same time, lasting all afternoon.

So what are we actually drinking when we drink tea? And what does it do to our mind? The short answer is two key players, working as a team. Here's the slightly longer answer, without the lab coat.

Inside the leaf

A tea leaf holds more than 2,000 compounds (LPI), while caffeine and L-theanine do most of the work on your mind. One pushes, the other steadies.

1. Caffeine, the engine

First, a myth to bust. There is no such thing as "theine". In 1827 a chemist named Oudry isolated a stimulant from tea and gave it its own name. By 1838, the chemists Mulder and Jobst had shown it was simply caffeine (Latosińska and Latosińska, 2017). Same molecule in your espresso, your energy drink and your gaiwan. So when people talk about the effects of theine, they mean the effects of caffeine in tea.

Here's how it works. Through the day, your brain builds up a molecule called adenosine, which acts like a brake and makes you feel tired and sleepy. Caffeine has a similar shape. It sits in adenosine's seat on your brain cells, so the brake signal never lands (LPI). You feel awake.

Now a fact that surprises most people. Gram for gram, dry tea leaves usually hold more caffeine than coffee beans. A 2022 survey of 1,398 tea samples from 17 Chinese provinces found average caffeine contents from 2.7% for oolong to 4.3% for yellow tea, with green, red (black), white and dark teas in between (Food and Chemical Toxicology, 2022). Arabica beans hold about 1.3%, and robusta roughly double that. Roasting barely touches caffeine, so roasted and raw beans come out about the same (Ludwig et al., 2014).

So why does a cup of coffee often hit harder? It depends on how you brew. A Western-style cup of tea uses a couple of grams of leaf for a big mug, so the caffeine is spread thin. Gongfu cha is different. We use a lot of leaf in a small gaiwan, sometimes with boiling water, so a full session can add up to as much caffeine as an espresso, or more. The difference is pace. An espresso delivers its whole dose in a few sips. A gongfu session releases it in small cups, infusion after infusion, over an hour or two, with L-theanine riding along (more on that in a moment). Same molecule, different rhythm.

Caffeine itself isn't the villain. In moderate amounts, from coffee or tea, it's a reliable pick-me-up. It's the dose that matters. The effects of energy drinks on the body show what overdoing it looks like, with jitters, a racing heart, anxiety and bad sleep. In tea, though, caffeine never works alone.

2. L-theanine, the steady hand

L-theanine is an amino acid that makes up about 1 to 2% of a dry tea leaf (LPI). It is also behind the savoury, brothy sweetness of a good green tea.

Here's the fun part. It barely exists anywhere else in nature. Outside the tea plant (Camellia sinensis), it has only been found in two ornamental camellias and one mushroom, the bay bolete (BfR). In practice, if you are getting L-theanine from food, you are drinking tea.

Your body absorbs nearly all of it, and it crosses into the brain (LPI). There it boosts alpha waves, the brain rhythm of being relaxed but awake, like the moment you close your eyes and settle. In one study, just 50 mg of L-theanine raised alpha activity compared with a placebo (Nobre et al., 2008).

3. The magic is in the mix

On their own, each compound does something. Together, they do the thing you actually feel.

In one study, 50 mg of caffeine plus 100 mg of L-theanine made people faster and more accurate when switching between tasks, and less easily distracted (Owen et al., 2008).

Brain scans show why. In an fMRI study, L-theanine reduced the brain's response to distractions. Combined with caffeine, it also quietened the default mode network, the set of brain regions that lights up when your mind wanders off (Kahathuduwa et al., 2018). Less noise, more signal. That's why we see tea as a natural energy drink. A sugar-free energy drink, minus the crash.

Not every tea hits the same

The crew is always there, but the line-up changes from tea to tea. That's why one tea is an energising tea that feels like a sunrise, and another feels like a warm blanket.

It starts on the plant. Caffeine concentrates in the buds and youngest leaves (LPI). Stems carry much less. One study measured about 56% less caffeine in stems than in buds and leaves (Cranfield University). Yet stems hold more L-theanine than leaves (Foods, 2022). That's why stem tea (kukicha) makes such a mellow evening cup, with low caffeine and plenty of theanine.

Then comes processing. Caffeine is fairly stable whatever happens to the leaf. L-theanine is more fragile and tends to drop as oxidation and fermentation go further. In one analysis, infusions of Shou (Cooked) Pu'Erh Tea held far less L-theanine than green or red tea, while caffeine stayed comparable (Ayakdaş and Ağagündüz, 2025). So each tea brings its own balance, and its own mood. Science hasn't mapped all of it yet, and other compounds like tea polyphenols, theobromine (also found in chocolate) and GABA join the party too.

And then there's you, at the kettle. Hotter water and longer steeps pull out noticeably more caffeine, while L-theanine stays fairly steady (Ayakdaş and Ağagündüz, 2025). Want it calmer? Go cooler and shorter.

To help you pick your mood, we note the body feel on the packaging and product page of every tea we select. Treat it as a rough guide rather than a promise. Bodies differ, and some people are naturally more sensitive to caffeine than others, so the same tea can feel gentle to one person and lively to the next.

And if you're after a caffeine-free tea, there isn't one, unless it's been decaffeinated. Every tea from the tea plant is a caffeinated tea (LPI). Herbal infusions are caffeine-free, but they aren't tea.

Pour one, see for yourself

An engine (caffeine) and a steady hand (L-theanine), tuned by the plant, the craft and the way you brew. That's the whole trick. No alcohol, no sugar, just tea.

If you're doing Dry January, or just drinking less, keep in mind that tea is the non-alcoholic beverage that actually does something. It's as social as a beer and lasts all evening.

Still, all the studies in the world won't replace a session. It's better experienced than explained. Grab a gaiwan or a Chinese tea set, pick a high-quality tea from our shop, or come and find us at our next pop-up. We'll pour.