How do Caffeine Theanine Interactions Affect Mood and Attention? Caffeine/Energy Drinks in the News

We associate caffeine with being hyper and tea with being calm, so what happens when a person has caffeine and theanine together?  I reviewed a paper by the Department of Psychology at Tufts University in which they gave 36 people caffeine, theanine, or both. These participants had to watch disturbing episodes of Band of Brothers to get them all emotional, then take tests to rate their mood and attention. The results indicate just how well theanine and caffeine play together (or against each other).

But first… Materials and Methods

On the day of the experiment, study participants were given one of four treatments:

  1. 200 milligrams caffeine + 200 milligrams theanine = “C + T”
  2. 200 milligrams caffeine + 0 milligrams theanine = “C”
  3. 0 milligrams caffeine + 200 milligrams theanine = “T”
  4. 0 milligrams caffeine + 0 milligrams theanine (placebo control)

Neither the scientists nor the participants knew which treatment they were getting because the caffeine and theanine were given in pill form. This is what’s called a double-blind, repeated-measures design. The way the study went, each participant went through all four treatments on different days. This is important because people react to caffeine in different ways, so you can’t base your experiment results on the assumption that people react to caffeine the same way. Instead, you want to compare how a particular person handled all four different treatments.




When people got the C + T pills, they reported increased tension, depression, anger, confusion, and total mood disturbance compared to the placebo. This result is surprising because it suggests the calming influence of theanine was totally overshadowed by the effects of caffeine. In fact, the only mood profile where theanine made a difference was vigor. For whatever reason, people who took the C+T pills reported feeling less vigor than the people who took the caffeine pills.




Other studies before this one have found caffeine increases our attention on the big picture while theanine increases our attention on the details. This is called global processing bias and local processing bias. Global processing bias means you might pay more attention to the size and shape of a mountain while local processing bias means you might pay more attention to the jagged cliffs and random tree clusters on that mountain.

In this study, the caffeine pills gave the participants a bias toward global attention, and the theanine pills gave the participants a bias toward local attention…just like the other experiments in the past had suggested.

*Scientists high-five! the experiment worked as it was supposed to*


When the participants had the C+T pills, the caffeine and theanine canceled each other out, and the attention bias was no different than placebo!




Imagine you were holding a picture where one medium-sized arrow was pointing left, but it was surrounded by dozens of smaller arrows pointing right. This is a rough description of the Attention Network Test (ANT). The ANT measures a few different types of attention. One of those is called the Executive Control Network Function.

Executive Control Network measures the extent to which incongruent-relative-to-congruent arrows interfere with determination and response.

I wonder if it’s called “Executive Control” because if you were an executive of a company you’d have to ignore lots of bad ideas surrounding one good idea and act upon it quickly…

When participants had the caffeine pills, they showed the best executive control. Having theanine (without caffeine) gave the participants the worst executive control. When participants had T+C pills, caffeine and theanine canceled each other out, and the result was no different than placebo.

Does that mean if you’re an executive or someone who needs to have a strong BS meter, you should avoid theanine…?

Apparently being in an emotional state really makes a difference whether theanine helps or hinders your executive control. In calm situations, theanine can help the same way mindfulness and meditation improve Executive Control scores. However, this was not a calm situation. The participants in this study were all triggered into an emotional state beforehand, and, in this state, the calming effects of theanine can be counterproductive. Theanine in stressful situations is like listening to a slow-dance song while you’re sprinting.



The Limit Does Not Exist - Mean Girls
This is a Mean Girls reference…

All results from this study came from stressful situations. There was no second round of trials where the participants were fed caffeine, theanine, or C+T pills and allowed to sit quietly for their tests.

How great would it be to redo this study and show these same participants episodes of Bob Ross?

Ideally, we could compare the way C+T pills affect people’s moods when they are stressed out and emotional versus when they are calm and happy. But this study only looked at the stressful situation, and other similar studies have only looked at calm situations.




Yes, cheating is bad, but it’s kind of a big deal when one scientist is able to copy another scientist’s experiment AND get the same results. When an experiment is reproducible, it suggests the results of that experiment are not a fluke. This is why scientists talk about what other scientists have done when they’re sharing their own results.

There have been other experiments on the effects of caffeine and theanine on attention and cognitive processes. That’s the good news. The bad news is that they’re inconsistent. Here are some of the findings from other studies:

  • 100 mg caffeine + 46 mg theanine improved attention task switching compared to placebo
  • 40 mg caffeine + 100 mg theanine improved attention task switching compared to placebo
  • 50 mg caffeine + no theanine improved attention task switching compared to placebo
  • 50 mg caffeine + 100 mg theanine reduced errors on sustained attention tasks, but only caffeine reduced response times
  • 150 mg caffeine + 250 mg theanine reduced response times but only caffeine reduced errors

Wait, what? So does theanine really help or is it caffeine doing all the work? Those last two contradict each other! AHHH! How come TV-show scientists never have this problem?

The takeaway message here is that the interactions of caffeine and theanine aren’t always consistent. This study shows that in stressful situations where emotions are running high, theanine is not going to counter the increase in tension, anger, and confusion. Theanine is not going to help you pause the situation, calm down and think. In fact, theanine might make your thinking and reactions worse than if you just had caffeine alone.


What are your thoughts? How do caffeine and theanine combinations affect you?

You can share your comments below or chat me up on Social Media.

Let’s chat!


  1. Caffeine and theanine exert opposite effects on attention under emotional arousal
    Grace E. Giles, Caroline R. Mahoney, Tad T. Brunyé, Holly A. Taylor, Robin B. Kanarek
    Canadian Journal of Physiology and Pharmacology, 2017, 95(1): 93-100,

Read more from the caffeine/energy drinks in the News series – here


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