top of page

Theanine: What It Is & What It Can Do

Updated: Feb 17

Theanine is an amino acid commonly found in tea and certain mushrooms. In functional medicine, theanine has a long history of use for anxiety. Theanine may be supportive for anxiety, stress, sleep, focus, attention, immunity, inflammation, blood pressure, cardiovascular health, and tumors. New research suggests that theanine may also offer support for mast cells and histamine intolerance.

In this article, I want to discuss the benefits of theanine. You will learn about some better-known health benefits of L-theanine, including stress, anxiety, sleep, and immune health. More importantly, I will share how L-theanine may be beneficial for histamine intolerance and mast cell activation syndrome combined with other mast cell stabilizers.

What Is Theanine?

Theanine is a type of amino acid. It is found in tea and certain mushrooms. There are two different forms of theanine: L-theanine and D-theanine. L-theanine is the more common form used for all kinds of health benefits, including stress, mental health, and immunity.

Theanine is not to be confused with threonine, another amino acid spelled in a similar way. Theanine is similar to another naturally occurring amino acid called glutamate. The role of glutamate is transferring nerve impulses in your brain. Theanine has the ability to act like glutamate too. Thus it can affect brain chemical dopamine, serotonin, and GABA levels, brain health, and mental functions. It may also block the activity of glutamate.

Benefits of Theanine

L-theanine has several potential health benefits. Here are the main benefits of theanine:

Stress and Anxiety Relief

L-theanine may offer relief from stress and anxiety. According to a 2008 study published in the Asian Pacific Journal of Clinical Nutrition, theanine in tea may help to relax your mind without causing drowsiness and may help to improve mental alertness (1). According to a 2016 review published in the Journal of Nutrition & Intermediary Metabolism, l-theanine may help to reduce stress and anxiety during stressful situations (2). A 2009 study published in the Journal of Clinical Psychiatry has found that l-theanine may even be beneficial for those with schizophrenia or schizoaffective disorder by reducing anxiety and improving general functioning (3).

Improved Focus and Attention

L-theanine may also help to improve your cognition, focus, and attention, especially when combined with caffeine. A 2010 randomized controlled trial published in Nutritional Neuroscience has found that the combination of 97 mg of L-theanine and 40 mg of caffeine has helped to improve alertness and cognitive performance and to reduce fatigue in young adult participants (4).

Better Immunity and Lower Inflammation

L-theanine may offer benefits for your immune health as well. According to a 2016 review published by MDPI, L-theanine may lower the risk of respiratory tract infections and may support a healthy immune system (4). A 2011 study published in the Journal of Nutrition has found that theanine and catechins in green tea may help to reduce the risk of flu (5). Moreover, a 2020 study published in the Journal of Functional Foods has found that l-theanine may have anti-inflammatory effects in the intestinal tract (6).

Improved Blood Pressure and Cardiovascular Health

L-theanine may also be beneficial for you if you have high blood pressure. Since high blood pressure is a major risk factor for cardiovascular disease, L-theanine may be great for your heart too. A 2012 study published in the Journal of Physiological Anthropology has found that L-theanine may help to reduce stress and related high blood pressure (7). According to a 2016 review published by MDPI, L-theanine may help to improve resting heart rate and blood pressure (4).

Better Sleep and Relaxation

By supporting relaxation and reducing stress, L-theanine may also help to improve your sleep. According to a 2016 review published by MDPI, L-theanine may promote relaxation and support sleep (4). A 2011 randomized clinical trial published in Alternative Medicine Review has found that taking 100 mg of L-theanine twice a day for 6 weeks has helped to improve the sleep quality of children (ages 8 to 12) with attention deficit hyperactivity disorder (ADHD) (8).

Reduced Risk of Tumors and Cancer

L-theanine may also offer anti-tumor effects that may reduce your risk of cancer or may support cancer treatment. According to a 2006 study published in Cancer Epidemiology, Biomarkers, and Prevention, L-theanine may help to support chemotherapy treatment (9). A 2004 study published in the International Journal of Cancer has found that drinking green tea, which is high in L-theanine, may reduce the risk of ovarian cancer (10). A 2012 study published in Cancer Epidemiology has found a link between drinking tea and a lower likelihood of developing pancreatic cancer (11).

Theanine, Histamine Intolerance, and Mast Cells

Before we get into the relationship between theanine, histamine, and mast cells, I want to talk about histamine intolerance and mast cell activation syndrome.

What Is Histamine Intolerance

Histamine is a natural chemical in your body that supports your immune system by getting rid of allergens. Histamine also plays a role as a neurotransmitter between your brain and other parts of your body, supporting your mental and brain health. It releases hydrochloric acid for digestion.

Though histamine is essential for your health, too much histamine can become a health issue. Too many high-histamine foods, stress, anxiety, poor sleep, environmental toxins, and other factors can lead to increased histamine release. If your body is unable to keep up with all this extra histamine, it will lead to histamine buildup. This histamine buildup called histamine intolerance can affect your entire body and cause widespread symptoms.

Symptoms of Histamine Intolerance

Symptoms of histamine intolerance may be widespread, may seem unrelated to each other, and may be anywhere from mild to severe.

Symptoms of histamine intolerance may include:

  • Headaches and migraines

  • Eczema, dermatitis, acne, and other skin issues

  • Hives

  • Fatigue and sleep issues

  • Red eyes

  • Dizziness or vertigo

  • Heart palpitation or racing heart

  • Brain fog, confusion, memory issues

  • Irritability and mood swings

  • Anxiety or panic attacks

  • Allergies

  • Asthma

  • Congestion, runny nose, or

  • Acid reflux, bloating, diarrhea, and other digestive symptoms

  • Abnormal menstrual cycle and premenstrual syndrome (PMS)

What Is Mast Cell Activation Syndrome

Your mast cells are a type of white blood cells in connective tissues, including your digestive tract, skin, respiratory tract, urinary tract, reproductive organs, surrounding your nerves, and near your blood vessels and lymph vessels. They are in charge of storing histamine and other inflammatory mast cell mediators. If you are exposed to an allergen, chemical, foreign pathogen, or other triggers, your mas cells will release these inflammatory mediators to fight invaders and protect your body. Though your mast cells are essential for a healthy body, overactive mast cells can increase your risk of mast cell disorders, including mast cell activation syndrome (MCAS). MCAS is a complex health condition that can cause chronic inflammation and widespread symptoms.

MCAS vs Histamine Intolerance

Though mast cells and high levels of histamine play a role in both histamine intolerance and MCAS are not the same. If your body has too much histamine due to a high-histamine diet, stress, poor sleep, toxins, certain medications, or other histamine-promoting factors, and it cannot break down excess histamine, sometimes related to genetic factors, you can develop histamine intolerance. In MCAS, when your mast cells are triggered by allergens, mold, toxins, certain medications, stress, pain, lack of sleep, or other triggers, they will trigger an immune response, and your mast cells will release histamine (and potentially many other pro-inflammatory mediators) resulting in symptoms. MCAS can be a cause or even the primary cause of histamine intolerance. However, MCAS is not the only cause. Also, you can have MCAS without symptoms of histamine intolerance. Though many people experience both conditions, it’s possible to have only one of these conditions.

Symptoms of Mast Cell Activation Syndrome

You may notice that many symptoms of MCAS are similar to histamine intolerance. Just like with histamine intolerance, symptoms of MCAS may vary from person to person.

Your symptoms of MCAS may include:

  • Rashes, eczema, and other skin issues

  • Hives

  • Itching

  • Low blood pressure

  • Heart palpitations

  • Chest pain

  • Headaches of migraines

  • Fatigue

  • Brain fog

  • Weakness

  • Dizziness

  • Loss of appetite or low appetite

  • Rapid weight loss or weight gain

  • Rhinitis

  • Gastrointestinal troubles, including abdominal pain, diarrhea, nausea, and vomiting

  • Nervous system symptoms, such as anxiety

  • Vision changes

L-Theanine, Mast Cells, and Histamine Intolerance

L-theanine is a calming neurotransmitter that helps to reduce stress and anxiety and supports sleep. Beyond high-histamine foods, high stress and poor sleep can fill up your histamine bucket quickly and contribute to histamine intolerance. Stress can also trigger mast cell activation causing MCAS symptoms. Furthermore, fatigue, poor sleep, anxiety, and respiratory symptoms are common symptoms of histamine intolerance. As you’ve learned in the earlier section, L-theanine may help to reduce stress and anxiety, support sleep, improve immunity, and reduce respiratory issues.

Though L-theanine is not directly a natural anti-histamine, by calming your nervous system, it can reduce mast cell activation, histamine intolerance, and histamine-related symptoms, especially fatigue, poor sleep, anxiety, mood swings, and respiratory symptoms.

According to a 2013 review published in the British Journal of Pharmacology, L-theanine may offer some anti-allergic activity (12). Researchers found that L-theanine may decrease histamine release from rat mesenchymal precursor cells (rMPCs) and human mast cell line-1 (HMC-1), may reduce the secretion of pro-inflammatory cytokines, and may help to stabilize your mast cells.

A 2011 study published in Amino Acids has found that theanine may help to stabilize mast cells and reduce mast cell histamine release (13). A 2016 study published in Food and Chemical Toxicology has found that L-theanine may help to reduce allergic response and inflammation of the airways in allergic asthma (14).

Though the benefits of L-theanine for mast cell activation and histamine intolerance are still under research, based on what we know, L-theanine may be beneficial for stabilizing mast cells and reducing histamine. L-theanine is generally safe without known side effects. I recommend combining L-theanine with a low histamine diet and other mast cell stabilizing foods and supplements for optimal health benefits. To learn about other mast cell stabilizers, I recommend reading my tips for stabilizing mast cells in this article.

Next Steps

Are you experiencing symptoms of histamine intolerance or MCAS? Are you interested in what treatment options are best for your situation? Working with a healthcare practitioner knowledgeable about histamine intolerance and MCAS is the best way to get to the root cause of your symptoms and create an individualized treatment. I welcome you to start a personalized functional medicine consultation with me for further guidance to improve your health. You may book your consultation here. Check out my Histamine Intolerance Course here. Learn on your own time, from anywhere. Get an inside look at the most helpful functional medicine tests for pinpointing imbalances, ways to identify and manage the most common (and sometimes surprising) mast cell triggers, and learn what to eat, what to avoid, and why.


What dosage of theanine is recommended to effectively block or reduce histamine?

bottom of page