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Written By: James Dixon

James has a Masters degree in Philosophy, has a background as a personal trainer, writes for various health and nootropics publications and is also a published author. All of his experiences and qualifications to date, mean he is incredibly well placed to test, research and review nootropics - which is his main role here at Peak Nootropics.

L-theanine is a form of the amino acid theanine, commonly found in certain teas and fungi. Amino acids are molecules that the human body uses to create protein. It needs a complement of 20 different amino acids to maintain good health and proper function.

These amino acids are combined together to create different protein strands. These in turn form the building blocks of life.

Theanine is akin to glutamate, another, naturally occurring amino acid that aids nerve impulse transmission within the brain. Theanine can act in a similar way, helping with this transmission, and, as a result, improving cognitive function. However, it can at times limit glutamate’s effects. It may also have an effect on several other brain chemicals, most notably dopamine, serotonin, and GABA.

L-theanine plays into this. It’s often used in nootropic supplements, or supplements designed to aid and optimize cognition, mental wellbeing, and brain health. It’s also often taken for stress relief and to overcome anxiety, though the clinical data are mixed on this – there is no conclusive support for its use to date.

What can l-theanine do for you?

There are actually quite a few promising uses for l-theanine, though more clinical data are generally needed before we can say so for sure. We can make a few tentative claims, however.

Stress and anxiety relief

L-theanine has been shown to potentially lower stress and anxiety levels. It’s a common component of tea, which has often been found to have relaxing qualities, both in studies and in the popular imagination.

The data back up l-theanine’s role in this regard, at least in a small way. Several trials have been able to link l-theanine use with lower levels of stress and anxiety in those experiencing adverse situations. It has also been shown to diminish the effects of anxiety on those suffering with schizophrenia or schizoaffective disorder, as well as enabling better symptom management.

More data are needed, of course. However, it’s a good bet at this stage that there is a fair amount underlining the case for l-theanine as an anti-anxiety, stress relieving supplement. It is, after all, one of the main reasons we often see it in nootropic supplements.

Sleep quality

As part of this stress and anxiety reduction, there is a lot of data showing that l-theanine can help you get a better night’s sleep.

Animal and human studies have found that doses of both 250 mg and 400 mg of l-theanine can lead to much improved sleep quality. Doses of 200 mg of l-theanine have also been found to lower resting heart rates, a key component of relaxation, and of relaxing for sleep.

L-theanine has also been shown to help those diagnosed with attention deficit hyperactivity disorder (ADHD) to sleep better. Specifically, a study looked at boys aged 8 to 12 with ADHD diagnoses who were given two 100 mg doses of l-theanine daily. They experienced more restful, longer periods of sleep compared to a placebo group after six weeks.

Similarly, l-theanine has shown potential for use in treating those suffering with schizophrenia-induced insomnia. It has been shown to improve quality of sleep for those with diagnoses.

More work is needed to prove that this effect can be replicated, and that l-theanine is safe for long-term use, especially in children. However, it does seem incredibly promising – all of the above points to l-theanine as a potential, incredible sleep aid.

Focus and attention

This is the next reason we often see l-theanine used in common nootropic formulas – l-theanine shows promise as a way to improve focus and attention, especially when paired with caffeine or some other form of stimulant.

One small study from 2010 saw participants take a combination of 97 mg of l-theanine and 40 mg of caffeine (about two thirds of the amount you get in a single shot of espresso). Participants were all young adults subjected to demanding tasks. They were found to be better able to focus on the task than control groups, whilst also experiencing greater alertness and diminished fatigue levels.

Immune function

L-theanine may also help to improve immune health and function, though the research is a little thin, here. A 2016 study found that it was able to decrease infection to the upper respiratory tract, whilst one from 2011 showed that catechins from green tea (high quality antioxidants) combined with l-theanine shows promise for warding off the flu.

It’s also theorized that l-theanine may be able to improve intestinal tract inflammation, though more data are needed to verify this and build on these initial findings.

Cancer treatment

There has been some associated between l-theanine and an amplification of certain chemotherapy treatments’ tumor fighting effects. In effect, l-theanine may be able to make chemotherapy more effective and efficient at fighting cancer and reducing tumor size.

There is a correlation without any proven causation between tea drinking and lower risks from cancer. Those who regularly drink tea experience lower cancer rates, without the exact mechanism being understood. In fact, women who regularly drink green tea have been found to be over 30% less likely to develop pancreatic cancer than those who don’t drink tea. Some experts have put it in part down to the l-theanine content in tea.

Blood pressure

This is quite a big one, and it relates in part to l-theanine’s ability to keep you feeling calm under pressure. It may help to keep blood pressure levels low in stressful situations. This has been born out in part by clinical data. One study showed that l-theanine use could reduce the increase in blood pressure inherent to those attempting stressful mental tasks.

The same study demonstrated that caffeine might have a similar effect, if less pronounced.

Risks of l-theanine use

L-theanine is largely safe to use. However, there are a few circumstances in which you may want to take extra care. There are a few side effects and interactions to note.

Side effects

There are no known side effects associated with l-theanine consumption. It is safe to take without fear of major adverse symptoms, both as a tea and in supplement form. However, do take note that the Food and Drug Administration (FDA) isn’t responsible for regulating supplements. They do not look into them, do not sign off on them.

The onus is therefore on the manufacturer to ensure that supplements are high quality and safe, and on the consumer to ensure that they are buying from reputable companies.

There are also a few things to watch out for. Though l-theanine has been shown to have promising effects for those undergoing cancer treatment, teas than contain it may also contain additional ingredients that are less helpful. They can in fact be potentially harmful to those undergoing cancer treatment. For example, the polyphenol EGCG, commonly found in green tea, can stymie chemotherapy’s results, reducing bortezomib’s efficacy (a common chemotherapy drug).

Do always ensure that you talk to your healthcare provider when considering changing your supplement regime or using any kind of additional therapeutic methods, especially when undergoing treatment for any medical concern.

L-theanine supplementation itself should be healthy enough, all things being equal. However, if you rely on green tea for it, as many do, there are some side effects to be wary of. Too much green tea can mean too much caffeine, which can lead to mood swings, energy spikes and crashes, irritability, nausea, and insomnia, among other effects.

Additionally, if you are pregnant or breastfeeding, you should limit how much tea you drink. Opt for decaffeinated where you can. Once again, it’s always best to consult your doctor before changing your diet or supplement regime when you are pregnant.


You may experience moderate interactions between l-theanine and common antihypertensive drugs – medications for high blood pressure. This is because, as we have seen, theanine can work to lower blood pressure. In conjunction with an antihypertensive drug, your blood pressure may drop too far.

There is also a minor interaction to be wary of if you’re taking CNS depressants, or sedative drugs. Sedatives bring your breathing rate down and can cause sleepiness. Theanine may also cause these – we have seen how relaxing it can be, and this may extend further. Though there is no research showing that sedatives and theanine might interact to bolster one or another’s effects too far, it is still best to practice caution.

Dosing l-theanine

There is no agreed-upon dose for l-theanine. The research is at present too young. There isn’t enough data to be conclusive about it. However, most studies have used doses around of 200-400 mg daily, which seems to elicit the desired results.

Always practice caution, however. If you’re unsure about l-theanine, or about how much to take, do consult your doctor.

My final take

I’ve actually been using l-theanine quite passively for years now. This is because I’m a big fan of certain nootropics that include it as a matter of course in their formulae. In fact, I always question nootropics that omit it.

This is because it really does show a lot of promise. Largely, this promise relates to its anxiety fighting effects. This is where the data are arguably the most conclusive. It should keep you relaxed and stress-free, even when you regularly experience stressful situations, whilst also improving your focus and quality of sleep.

Then there are other, more niche benefits – fighting cancer, dealing with schizophrenia symptoms, helping with ADHD management. More research is needed. As ever, more research is always welcome. It allows for an ever-increasing amount of confidence and a diminished risk-factor.

However, for the moment, we can quite comfortably say that many of l-theanine’s purported benefits seem to have something to them. Certainly, its nootropic benefits seem quite solid.