Caffeine: it’s everywhere. Apart from alcohol, no other substance is as widely used and accepted by society as caffeine. From traditional sources like tea and coffee to energy drinks, to supplements found in the supermarket, caffeine is affordable, convenient, and effective. It has permeated the lives of the majority of people in the world – 90% of the world’s population consume some form of caffeine on a daily basis.
Caffeine, mainly in its beverage form of coffee, is used en masse by society, so much so that it is hardly even thought of as a drug. It is so casually consumed by most people that not much thought is given to how it works, how it can be beneficial, and how it can be potentially harmful.
It is well known that caffeine can carry with it several unpleasant side effects. Certain individuals can be more sensitive to caffeine than others, and some are more susceptible than others to these side effects. The most commonly reported side effects of caffeine include increased blood pressure , anxiety, jitters, and insomnia.  Luckily, many caffeine users have found a potential way in which these uncomfortable effects can be prevented. The answer comes in the form of one non-essential amino acid: theanine.
Theanine is a naturally-occurring amino acid found in various plants, mainly certain types of green tea. Only the L (“levo”, left)-enantiomer of theanine has been extensively researched for its effects in humans, and references to “theanine” typically imply only L-theanine.
The compound itself was first isolated from tea leaves in 1950 and has since gained widespread popularity as a dietary supplement. In the United States, it has been approved for over-the-counter use. Response to L-theanine in Europe has not been as favorable. The European Food Safety Authority (EFSA) has objected to claims of L-theanine being beneficial to cognition and stress, and it is not sold under any kind of health claims.
Perhaps the most alluring aspect of L-theanine comes with its ability to promote relaxation without being sedating. This property has led to its widespread use alongside caffeine. Potentially, the relaxing effects of L-theanine “take the edge off” of caffeine use by mitigating the jitters that come with caffeine, all while working alongside caffeine to improve cognition and alertness. It has also been found to reduce blood pressure, which is especially helpful for those who experience high blood pressure from caffeine use. 
After ingestion, L-theanine crosses the blood-brain barrier (BBB) with relative ease. Its effects set it within an hour from ingestion, and effects last for about 5 to 6 hours after administration. 
Theanine does not have a significant impact on increasing the levels of monoamines (i.e. serotonin) or catecholamines (i.e. norepinephrine) in the bloodstream. 
Because theanine is structurally similar to the neurotransmitters glutamate and glutamine, it competes with them at their transporters, which can reduce synaptic levels of glutamate, a dangerous neurotransmitter that causes neurotoxicity in high levels. 
Additionally, administration of L-theanine has been found to increase GABA levels in the cerebrum by nearly 20%. GABA is an inhibitory neurotransmitter, and this is largely thought to be a major contributor to Theanine’s anxiolytic and relaxing effects. However, research has not yet provided a conclusive answer to L-theanine’s exact mechanism of action.
While L-theanine is a respectable anxiolytic and cognitive enhancer in its own right, most users find it most effective when paired with caffeine, as mentioned above. To understand the power of stacking caffeine with L-theanine, it’s also important to know the way in which caffeine operates.
Caffeine’s stimulant properties come mainly from its action as an adenosine receptor antagonist. When adenosine receptors are activated by adenosine, it causes drowsiness in the individual. Adenosine accumulates naturally in neuronal synapses, and lower levels of adenosine translate to feelings of alertness and wakefulness. Because caffeine binds to adenosine receptors competitively, it inhibits adenosine from binding to the adenosine receptors, which in turn makes the body feels more awake. Of course, when caffeine is eliminated from the system, adenosine is once again free to bind to its natural receptors, returning the body to feelings of drowsiness.
Even though caffeine’s main effects are due to its adenosinergic mechanism, caffeine consumption also has an impact on other neurotransmitters. Caffeine (particularly in high doses) reduces the conversion of tryptophan to serotonin and this may exacerbate depression, especially if caffeine use is suddenly stopped. Therefore, 5-HTP, a serotonin precursor, can be used to counteract Caffeine withdrawal symptoms.
Stacking Caffeine & L-Theanine
The simultaneous use of caffeine and L-theanine appears to be the most common combination or “stack” of substances utilized by users of nootropics. Because both caffeine and L-theanine are cheap, well-studied, and generally accessible, it is a good starting point for those who are just getting into nootropics and cognitive enhancement. If you already use caffeine in any form, it wouldn’t hurt to see how L-theanine works for you.
Common combinations of caffeine and L-theanine are a 1:1, 1:2, 2:1, or 2:3 ratio of caffeine to theanine. The effectiveness of each ratio varies widely among individuals, so some trial and error might be necessary to find the right amounts. If you do not use caffeine regularly, it would be wise to start with a 1:2 ratio – that is, 100 mg of caffeine with 200 mg of theanine – and adjust from there. There is no “correct” way to stack the two, and it is mainly a matter of preference and personal brain chemistry.
Multiple studies using about 100 mg of L-theanine alongside 50 mg of caffeine demonstrated that the combination of the two had a fairly significant impact on cognition, even more so than either substance by itself.   L-theanine use in combination with caffeine also helps users remain focused on single tasks without being distracted by outer stimuli. 
Many nootropics are most effective when combined with other complementary substances. Researching different nootropics and their effects and benefits can be both fun and rewarding. However, sometimes the amount of information available makes it difficult to find a starting point. A combination of caffeine and L-theanine is the perfect starting point for anyone who is interested in nootropic supplementation and increasing their cognition. Because both compounds are well-studied both separately and in combination, it is a safe starting point for introducing people into the world of cognitive enhancement.
For those of you who don’t like messing up with powders (or just like the convenience of pills), try premixed Caffeine and Theanine caps
References [ + ]