Best L-Theanine Supplements: Top 10 L-Theanine Brands Reviewed

What Is L-Theanine

Theanine is an amino acid that is not typical for the popular diet because its natural sources are green and black tea and they are not the typical food from modern diets. 

Theanine does not belong to the essential amino acids and it is also not considered a nonessential amino acid. Theanine ranks alongside amino acids such as l-ornithine and l-citrulline.

The theanine structure resembles that of glutamine. It might be said that theanine is an ethyl derivative of glutamine. Theanine is a non-protein amino acid because it cannot be used for the body’s enzyme synthesis.

​​The richest theanine sources are green and black tea. The amount of theanine constitutes 3.1% of the weight of the dried leaves. The concentration of theanine in 200 ml tea may reach 25-60 mg.

​Theanine has always been associated with green tea because this tea is the richest source of theanine. This special amino acid is up to 50% of the total amino acids in green tea. 

It is interesting to note that the leaves of the young plants contain more theanine compared with the old ones. Various processes of processing also affect differently on theanine as fermentation reduces its levels, and drying increases the total percentage of theanine in tea.

Theanine can also be found in the Chinese camellia (Camellia japonica) and the porcini mushrooms Xerocomus badius, the latter being typical of the European continent.

The nutritional supplements industry uses theanine, which is chemically derived from glutamine by ethyl derivatives. Many of the conducted researches have used Suntheanine, which is patented theanine with 99% concentration of the active ingredient.

​How Does L-Theanine Work

​Theanine gets metabolized in the small intestine after oral intake. The metabolism is very similar to that of glutamine; as for the hydrolysis of the theanine, the glutaminase enzyme takes part. 

Its activity is strongest in the kidneys. After the breakdown, theanine uses glutamine peptides for distribution to other peptides. In addition to glutamine, l-theanine is structurally very close to the neurotransmitter GABA and also glutamate. 

It is known that theanine may cross the blood-brain barrier and to implement its physiological functions directly in the brain after oral intake. To reach the brain, theanine uses the leucine transport system. 

It was found that L-theanine reaches the brain in 1 hour after the intake and its activity is at its peak for the time of 5 hours. After the phase of strong activity, theanine gets cleared from the brain in the next 24 hours.

​The main function of theanine is associated with its effect on the brain and nervous system. Theanine is considered to be an antagonist of the excitatory receptor of n-methyl-d-aspartate and stimulates the levels of other neurotransmitters, such as GABA.

Its impact on serotonin and dopamine is still very controversial. Theanine is used for improving mood. It reduces stress but does not have strong sedative properties. 

​​It is said that it improves mental attitude and focus. Theanine can affect the taste buds in the way of suppressing bitter tastes.

Potential and Proven Benefits for People:

• The intake of L-theanine in doses between 50 and 250 mg by healthy individuals results in an increase of alpha waves within 45 minutes after oral intake. However, only the alpha 1 waves (8-10 Hz) get affected and not alpha -2 (11-13 Hz). Alpha waves are associated with a state of peace, selective attention and mental alertness. Another study even found that green tea with theanine increases theta waves and the results show the increased state of peace, more focus, and enhanced memory;
• Although the main function of theanine is not associated with the improvement of sleep, it can be effective under certain specific conditions. In children with attention deficit hyperactivity disorder (ADHD), intake of 200 mg theanine, 2 times a day, for 6 weeks in a row, can decrease activity during sleep by 10% and can also increase the quality of sleep. Theanine shows positive results in terms of another manifestation of ADHA, such as restless legs syndrome;
• The addition of 400 mg of theanine to standard antipsychotic drugs in people with schizophrenia and schizoaffective deviations leads to a sharp decrease in pathological symptoms and regulation of anxiety and aggression;
• Theanine successfully counteracts to anxiety and frustration. The effect is noticeable in individuals with high anxiety or under severe stress. In calm individuals, the effect is a little bit different than placebo;
• 200 mg theanine per day decreases the stress markers in humans. The theanine action is expressed is a decreased heart rate and a decrease of immunoglobulin A in acute stress, as well as in the overall attenuation of the sympathetic nervous system;
• In people with cognitive abnormalities, a 16-week intake of theanine and green tea enhances selective attention. This has been tested by the Stroop test;
• Theanine successfully increases levels of nitric oxide at relatively low concentrations, by stimulating the enzyme reactions and the eNOS enzyme. These properties lead to a vasodilatory effect and the improvement of cardiovascular health;
• Several studies have shown the positive effects of theanine on mood, mental attitude, and concentration. When in combination with caffeine, however, theanine demonstrates far more powerful results, expressed in increased accuracy and attention in cognitive tests, reduced fatigue, alertness stronger and shorter reaction time. Theanine also drastically reduces a headache, caused by high doses of caffeine.

Recommended Dosage​:

Daily doses in most studies vary between 100 and 200 mg daily. ​In some cases, the dose of 400 mg a day can be taken.

Higher doses show no risk of toxicity and short-term side effects, but there are sufficient data on the long reception.

How to Combine L-Theanine

​If the aim is the stimulation of mental attitude and focus, theanine gets successfully combined with caffeine, as the combination of both leads to better performance, compared to the individual user.

For combating stress and fatigue, theanine can be combined with adaptogens such as ashwagandha, Rhodiola, and Ginseng. For mood improvement, combination with 5-HTP is the appropriate choice.

For the quality of sleep improvement, the combination with melatonin, 5-HTP or GABA is recommended. The concomitant intake of theanine with glutamine is not recommended because they share the same road transport to the intestines and can compete for that.

The concomitant use of isolated l-theanine with green tea is not recommended because the latter can reduce the absorption of theanine drastically. In vitro studies establish two possible reasons.

The first is that natural theanine in green tea is more slowly absorbed and may prevent isolated theanine. The second is that the tannins in green tea suppress mitochondrial transporters, which are involved in the theanine metabolism.

Side Effects:

It is believed that theanine has very low toxicity, even at high doses. At this stage, tests have been based on 99% pure theanine and only done on animals - rats and monkeys. 

Toxicity tests in rats show that even high doses such as 6500 mg/kg body weight per day are not toxic. Long-term intake of 12 weeks also does not indicate any adverse effects. 

The longest legal test so far has been based on a daily dose of 4000 mg/kg body weight and has lasted 13 weeks, showing no toxicity. Tests on monkeys have shown that L-theanine has no carcinogenic activity. 

Short-term studies have also not indicated adverse effects on people. Detailed long-term studies are still missing.

The complete safety of theanine, when taken by pregnant women, nursing mothers and children is still not known. It is also not known if the intake of theanine is addictive.

Where Can We Find L-Theanine

L-theanine can be sold as a dietary supplement. It can also be found in its pure form or as part of a complex formula. In its pure form, isolated theanine with 99% concentration can be commonly found, as dosage varies between 100 mg and 200 mg per capsule.

Natural theanine can be found more rarely as part of a specialized green tea extract, as in this case, theanine can reach 50% of the extract. L-theanine gets offered less frequently as part of complex formulas.

Typically, the amino acid is added to the products improving mood, sleep and stress relief. Although on rare occasions, l-theanine is added to some sports formulas.

These may be pre-workout boosters (MuscleTech Nano Vapor), fat burner (MuscleTech Hydroxycut Elite) or formulas for midnight recovery (Animal PM and Ronnie Coleman Resurrect PM).

Theanine is one of many active ingredients in green tea, whom we can certainly call the great gift of nature. Theanine brings some of the most desirable properties of green tea which include mode, tone, and health improvement.

​Although being not as popular as an amino acid, the scientific basis behind l-theanine is stable enough to convince us to give a chance to this otherwise so valuable supplement.

If you choose l-theanine, do not expect it to replace the green tea. Use it according to its unique properties.