What is L-Theanine? The Health Benefits and Possible Side Effects

When it comes to amino acids, there are basically two types: the essential variant and the nonessential variant. Essential amino acids are produced by your body and, although you can certainly obtain them from outside sources, doing so would be for extra benefits – it’s not otherwise necessary. The nonessential amino acid is NOT produced by your body, which means you don’t need it – but they can confer great benefits when you obtain them from outside sources.

L-theanine falls squarely into the nonessential amino acid camp; it is found in certain mushrooms, as well as black and green teas. Because of its utility (which we will explain below), it is marketed in tablet or capsule form.

The Utility of L-theanine

In this article, I will list and analyze the multitude of health benefits for which L-theanine is known. Although it is usually considered to be one of the best sources of natural relaxation, it actually has a laundry list of features that are useful:

Relieves stress and anxiety

It should come as no surprise that L-theanine is mostly found in black and green teas – after all, these are widely prized for their ability to put you into a state of relaxation. Unlike the case with other substances that might promote bodily ease, L-theanine is able to do so without inducing drowsiness.

Another considerably important attribute of L-theanine was discerned in a mental health medical research trial involving people who were beset with schizoaffective disorder as well as schizophrenia. The startling results were published in the Journal of Clinical Psychiatry: L-theanine dramatically diminished the anxiety that is almost pervasively associated with these mental health disorders. Additionally, the amino acid was able to assuage the symptoms resulting from these.

The above results are only surprising due to the general severity of schizoaffective disorders. In truth, a prior review of a multitude of controlled research trials show that L-theanine was responsible for helping to reduce anxiety and stress in most of the (80% to be more exact) of the participants when they were presented with stressful situations in the trial.

L-theanine Improves Focus

If you are into using pre-workout supplements and powders, then you’ve likely seen L-theanine coupled with caffeine in the brands marketed as stimulants. There’s a reason for this, and it comes from a multitude of studies done with both caffeine and L-theanine: the results strongly suggested that the combination helps improve both attention and focus.

More specifically, one of the studies targeted young adults who were presented with demanding tasks. Beforehand, there were given a supplement containing 40 mg of caffeine (slightly less than half of the amount of coffee in an 8 ounce cup of coffee) and 97 mg of L-theanine. By the metrics of the study, it was ascertained that the participants were able to focus better, felt less tired and were more alert.

Enhanced General Immunity

There’s a lot of research showing the benefits that L-theanine confers on to the body’s immune system. One in particular, although somewhat conservative, seemed to show a positive correlation between L-theanine use and reduced information in the intestinal tract. More studies are underway to duplicate this result, and to push the extent of applicability.

If you are a drinker of green tea, then you’re in luck: another of the studies showed that the antioxidants found in green tea, when combined with L-theanine, can keep the flu at bay. The third study involving the effects of L-theanine on immunity was published in the journal Beverages; apparently, infections in the upper respiratory tract can be managed by L-theanine.

Although more studies need to be conducted to better verify the results, the ones that have been conducted thus far strongly suggest that L-theanine is useful for assuaging inflammation that occurs in the intestinal tract.

L-theanine for Blood Pressure

Because of its ability to dampen the effects of stress, L-theanine has shown promise for the management of blood pressure (as in, a tendency towards increased blood pressure). One study in particular analyzed cognition-related rises and blood pressure; the participants were given some L-theanine, and found that the amino acid dampened the rise in blood pressure associated with the mental tasks. For reference, it was able to outperform caffeine when this was given to the study participants.

Because of this and other research studies, L-theanine may be useful for engendering a good night’s rest due to its ability to induce relaxation. More specifically, separate doses of 250 mg and 400 mg of the amino acid L-theanine were found to dramatically improve late-night sleep in both human and animal subjects. Specifically, the lower dose of L-theanine actually diminished the resting heart rate – which conclusively proves its ability to induce relaxation

Yet another study specifically targeted young boys between the ages of 8-12 years of age. Some of these boys were chosen randomly to receive 200 mg of L-theanine per day – divided into two separate doses of 100 mg at even intervals. When compared to the rest of the boys who were given placebos, the ones who took the L-theanine consistently experienced lengthier and more restful sleep. Overall, this particular study took six weeks.

As for future indications based on present results, there seems to be a lot of promise that L-theanine can facilitate sleep in young boys (the only ones tested to date) who are beset with hyperactivity and attention deficit disorder. There have also been research indicators that L-theanine can confer the same sleep benefits to people with schizoaffective disorders and schizophrenia.

Can L-theanine Be Effective for Cancers and Tumors?

When coupled with specific chemotherapy drugs, L-theanine has shown an ability to elevate the anti-tumor properties of said drugs; as a result, researchers hypothesize that L-theanine has a lot of future potential in cancer therapy – as long as it is used in an auxiliary or supportive capacity.Backing this up somewhat, it has long been both anecdotal reports and a few studies showing a positive correlation between frequent drinkers of green tea and black tea and reduced rates of cancer.

In fact, in China there was a particular study involving women with ovarian cancer. They reported that of these women, the ones who imbibed one or more cups of green tea per day had longer lifespans. More work needs to be: this, of course, since it could also be that green tea drinkers tend to have more habits conducive to lengthening their lives.

Things to Watch Out For: L-theanine Side Effects

Although the general observed sentiment concerning L-theanine is its consummate safety when included in supplements and green or black teas, any users should also be advised that the FDA (Food & Drug Administration) does not regulate L-theanine or other supplements. So although there aren’t any direct side effects reported by consumers, this leaves it in the hands of the manufacturers and producers when it comes to ascertaining the safety of their products.

Even keeping in mind the research studies that have produced positive outlooks in regards to L-theanine anti-tumor abilities, it’s also known that cancer patients have to be wary of some of the other ingredients that are often concomitant with various teas containing the nonessential amino acids as well as essential amino acids.

The reasoning is elucidated by medical researchers at the Memorial Sloan Kettering Cancer Center. They found that one of the pervasive ingredients in green to the, a specific strain of polyphenol, is known to attenuate the effectiveness of some popular chemotherapy drugs. Therefore, before taking L-theanine supplements with a variety of other ingredients, you should always speak with your healthcare provider – particularly if you are aging of green or black teas.

There’s another noteworthy caution in regards to L-theanine. Sincerely usually combined with caffeine, if you imbibe large quantities the black or green teas containing it, you can experience certain side effects:

  • irritability
  • stomach discomfort
  • nausea

As is usually the case with supplements and the like, if you are a woman who is breast-feeding her pregnant, you should significantly limit consumption source to avoid having too much caffeine in your system. It’s always best to consult your physician with respect to such things.


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