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Overview: Theanine is found in various teas and is also available over the counter as a dietary supplement. Many products that naturally contain theanine also contain caffeine. Theanine is used for many different reasons, but its benefits are not well defined. Common side effects may include sleep changes or upset stomach. Before taking theanine, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is theanine used for?

Theanine is used for various reasons, but its benefits are not well defined. Some common reasons that people use theanine include the following.

Note: The FDA has not reviewed theanine for safety and effectiveness. Learn more about dietary supplements here.

How does theanine work (mechanism of action)?

Theanine is an amino acid that is naturally found in a plant called Camellia sinensis. The leaves of this plant are used to make many common teas, including green tea, black tea, and oolong tea. Theanine is found in these teas and in many other products made from Camellia sinensis, such as green tea dietary supplements. Dietary supplements containing theanine can also be made in a lab. Product labels may list theanine as L-theanine, which is the same thing.

Theanine seems to work as an antioxidant in the body. It also seems to reduce inflammation (swelling). In the brain, theanine can help protect your cells from damage and may also change the levels of certain brain chemicals, such as gamma-aminobutyric acid (GABA). Although this has led to interest in using theanine for improving mental performance and mood, reducing sleep problems, and helping with attention and focus, the benefits of theanine for any use are not well defined.

How should I store theanine?

You should store theanine according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of theanine?

The most common side effects of theanine are listed below. These side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.

  • Sleep changes
  • Upset stomach

There may be side effects of theanine that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of theanine?

While less common, the most serious side effects of theanine are described below, along with what to do if they happen.

Severe Allergic Reactions. Theanine may cause allergic reactions, which can be serious. Stop taking theanine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching or skin rash
  • Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Warnings & Precautions

Who should not use theanine?

Allergies to Ingredients. People who are allergic to any of the following should not take theanine.

  • L-theanine
  • Theanine
  • Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific theanine products they stock.

What should I know about theanine before using it?

Theanine is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.

Keep theanine out of the reach of children.

Some people use theanine for sleep problems. If you have trouble sleeping, it is important to make sure that you have the right sleeping conditions and good sleep-related habits. This is known as good sleep hygiene. Learn more about sleep hygiene here.

Some dietary supplements and foods that contain theanine also contain caffeine. For example, teas that naturally contain theanine naturally contain caffeine as well. Many theanine dietary supplements that are marketed for improving memory and thinking skills may also contain caffeine. However, dietary supplements and non-soda beverages are not required to state their caffeine content. Use these products with caution, especially if you are sensitive to caffeine or you regularly drink caffeinated beverages. Too much caffeine can increase your risk for side effects.

The FDA has not tested theanine products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using theanine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know whether theanine is right for you.

In particular, make sure that you discuss any of the following.

Other Medicines and Supplements. Theanine may interact with other medicines and supplements. Before taking theanine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how theanine could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if theanine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does theanine interact with foods or drinks?

There are no known interactions between theanine and foods or drinks. But many products that contain theanine also contain caffeine. It may be best to take theanine with a non-caffeinated drink and to limit your total caffeine intake while you are taking theanine.

It is unknown if drinking alcohol will affect theanine, but drinking alcohol while taking theanine may increase your risk for sleep problems.

Does theanine interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any sleep medicines before taking theanine.

The interactions between theanine and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with theanine is incomplete. Always check with your health care provider before taking theanine with any medicines.

Overdose/Missed Dose

What should I do if I accidentally use too much theanine?

If you or someone else has used too much theanine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Theanine is naturally found in teas such as green tea, black tea, and oolong tea. It is also found in dietary supplements. Read the product label closely and speak with a health care provider about how to use theanine safely. Do not take double or extra doses, even if you miss a dose.