What You Should Know About L-Theanine

Rising curiosity of L-theanine is flooding the health world. But what exactly is L-theanine? Here is what you should know.


L-theanine is an amino acid, a building block for proteins, naturally sourced from tea leaves and manufactured into supplemental form.

The amino acid is commonly explored in managing and preventing a number of health conditions, including anxiety, high blood pressure, and cancer, along with supporting

While L-theanine appears to be safe in the short-term, its use also bares moderate warnings regarding drug interactions.

L-Theanine Benefits and Uses

Improve Sleep

Low-caffeinated tea itself has been suggested to induce and improve sleep patterns. But L-theanine may also increase the release of GABA, a neurotransmitter that promotes relaxation and helps the body fall and stay asleep.

Unlike GABA, glutamate is an excitatory neurotransmitter in the brain that keep us alert. However, L-theanine is suggested to block glutamate, which may further employ the amino acid’s link to sleep improvement.

Complementary evidence published in the Journal of the American College of Nutrition found the administration of 200 milligrams (mg) of L-theanine before bed may support improved sleep quality without inducing daytime drowsiness.

Furthermore, a study published in Alternative Medicine Review demonstrated 400 mg of L-theanine on a daily basis granted a safe and effective in improving some aspects of sleep quality in boys diagnosed with attention-deficit/hyperactivity disorder (ADHD).

Relieve Anxiety

Similar to the pattern detailed to improve sleep, L-theanine has been considered to cause anti-stress effects by reducing excitation of neurons in the brain.

The increased GABA ultimately increases brain levels of dopamine and reduces serotonin, resulting in greater feelings of tranquility, calmness, and overall well-being.

Manage High Blood Pressure

A study published in the Journal of Physiological Anthropology found L-theanine not only reduces anxiety, but also reduces blood pressure increases in high-stress-response adults. This was the first study to research both L-theanine and caffeine under conditions of acute psychological and physical stress.

Ultimately, study participants with high blood pressure significantly decreased their levels while taking 200 mg of theanine daily for seven days compared to those participants in the caffeine plus placebo group. 

Reinforce Brain Health

According to the Alzheimer’s Drug Discovery Foundation, L-theanine might be beneficial in reinforcing brain health, particularly with a potential to improve attention and alertness in combination with caffeine.

Research suggests L-theanine has modest and short-term, yet positive effects on cognitive function, with some evidence supporting L-theanine has a significant effect on the general state of mental alertness or arousal.

Boost the Immune System

While the evidence is somewhat modest, a study published in Nutrition Reviews indicates intervening with L-theanine intervention enhances immune function. Furthermore, supplementing with capsules containing L-theanine and catechins has been shown to decrease the incidence of cold and flu symptoms.

Furthermore, L-theanine may enhance gammadelta (γδ) T cells, which are primarily found in epithelial tissues, where they have crucial roles in tissue repair and protect against infection.

Prevent Against Cancer

While the hunt for the cure for cancer lives on, the American Association for Cancer Research suggests L-theanine may be used as an effective chemo-preventive agent.

Supporting evidence implies theanine may have the wide therapeutic and/or adjuvant therapeutic application in the treatment of human lung cancer and leukemia, along with showing to induce apoptosis in breast, colon, hepatoma and prostate cancer cell lines, and to inhibit tumor cell migration in a report published in Molecules.

Support Weight Loss and Maintenance

There has been vast interest in the role of green tea on weight loss and maintenance related to its thermogenic property, or the metabolic process in which the body burns calories to produce heat, showing to facilitate weight loss by increasing calorie burn.

An animal study further found both caffeine and theanine were responsible for the suppressive effect of green tea powder on body weight increase and fat accumulation.

But aside from the direct link, L-theanine may also play a role in weight maintenance in a more round about way, including its benefits on anxiety and sleep, two factors that have a significant influence on weight.

Safety and Side Effects of L-Theanine

L-theanine is generally well tolerated by healthy adults, particularly with evidence supporting its safety at the upper limit of 250 mg daily, with most studies using 200 mg per day. To put this in perspective and though dependent on the quality and preparation technique, a standard 200 milliliter cup of tea supplies an average of 24 mg.

WebMD does warn though, pregnant and breastfeeding, women should avoid use related to the scarcity of reliable data, while parents should consult with their child’s physician before beginning L-theanine use.

And while L-theanine negative side effects are uncommon, commonly used medications and supplements that may be moderately interfered by the amino acid, including:

  • Medications for High Blood Pressure (Antihypertensives). With L-theanine displaying benefit to lower blood pressure, taking the amino acid along with antihypertensives might cause blood pressure to go too low. Common antihypertensives include captopril losartan, valsartan, amlodipine, hydrochlorothiazide, and furosemide (Lasix).
  • Stimulatory Drugs. Taking theanine along with stimulant medications might decrease the effectiveness of stimulant medications, including Some stimulant drugs include diethylpropion, epinephrine, phentermine, and pseudoephedrine.

Ultimately, always consult with a physician before using L-theanine, along with any sort of supplement for that matter, to ensure quality of safety of the product.