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Does consuming L-theanine with caffeine, either in drink (like matcha) or in pill form, affect the half-life of caffeine?

All I can find about these substances ares claims that L-theanine slows the absorption of caffeine, or that it removes the jitters and crash associated to caffeine, as you can read here and here.

Can we jump to the conclusion that it probably increases caffeine's half-life? Are there studies on that? I cannot find anything on this topic.

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    – L.B.
    Commented Dec 18, 2020 at 19:58
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    I edited the question with prior research and references
    – João Bravo
    Commented Dec 20, 2020 at 1:39

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The mechanism of action of L-Theanine is not quite well understood and at some degree recent studies find themselves in contradictory with the results, nevertheless I think the essencial is this

Glutamate is a powerful excitatory neurotransmitter. It plays an important role in cognitive functions such as learning and memory due to its role in synaptic plasticity.

Now, L-Theanine

blocks the reuptake of glutamine and glutamate

and thus it will increase the concentration of glutamate in the synaptic cleft, prolonging the effect

The mechanism of action of caffeine at the Central Nervous System can be summed up to one thing

Adenosine

In general, adenosine has an inhibitory effect in the central nervous system (CNS)

Regarding Caffeine

Caffeine demonstrates antagonism of all 4 adenosine receptor subtypes (A1, A2a, A2b, A3) in the central nervous system

which means that caffeine will have an excitatory effect on the central nervous system.

They are both stimulants of the CNS, however when combining the two we have an interesting conclusion by the authors in this article so that

l-theanine can counteract the stimulatory effect of caffeine. In rats, after caffeine administration intravenously with theanine at the same dose, the stimulant effect of caffeine was blunted. Whereas given by normal dose of caffeine with a smaller dose of theanine administration resulted in excitatory effects of caffeine, which suggested a dose specific dual activity of theanine

In summary it depends on the dose.

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  • This quote makes me wonder: by "with theanine at the same dose, the stimulant effect of caffeine was blunted", do they mean that the rats behaved as if they had taken none of the substances, i.e. had their cognitive functions decrease again? Or do they mean the rats still had higher cognitive funtions, but were less jittery?
    – João Bravo
    Commented Dec 20, 2020 at 16:36
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    this conclusion comes from other article: Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat, they conducted the experiment using a modified electroencephalographic exam and the conclusions were based upon the brain waves readings
    – program
    Commented Dec 20, 2020 at 17:37
  • I have read it, but I do not have the background to analyse their results. Oh well... Thanks for the answer. Did you find anything regarding caffeine half-life increase by L-theanine?
    – João Bravo
    Commented Dec 20, 2020 at 21:25
  • regarding your question specifically, the half-life is basically the ln(2) divided by the elimination rate constant, so in that sense when we refer ourselves to the half-life of a substance we are addressing terms of metabolism. The article does not mention that interaction because they do not interfere with each other at the metabolic level such as using the same cytochrome enzymes or having an inhibitory mechanism. when at equimolar doses they behave as physiological antagonists (basically they have opposite actions) but the plasma concentration remains the same it doesn't disappear
    – program
    Commented Dec 21, 2020 at 0:00
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    and the same logic can be applied to the non-equimolar concentration used and described on the article, normal dose of caffeine with a smaller dose of theanine administration resulted in excitatory effects of caffeine they don't mean to say that the liver started to metabolize slower and thus the time of the drug in the body increases, what they mean is that there is a physiological agonism such that both mechanisms are acting in the same direction; and since the rate of elimination is the same the half-life also is the same
    – program
    Commented Dec 21, 2020 at 0:02

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