L-Theanine

Purported Benefits, Side Effects & More
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This information describes the common uses of L-Theanine, how it works, and its possible side effects.
Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.

What is it?

L-theanine is a chemical found in both green and black tea. It helps you relax by lowering stress and anxiety (strong feelings of worry or fear).

L-theanine supplements come as tablets, capsules, chewables, liquids, and powders.

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What are the potential uses and benefits?

L-theanine is used to:

  • Improve sleep quality
  • Reduce anxiety
  • Prevent cancer
  • Lower your risk of getting a stroke (when there is no blood flow to your brain)

L-theanine has other uses, but doctors have not studied them to see if they work.

L-theanine that you get from tea is safe. Talk with your healthcare provider before taking L-theanine supplements. They are stronger than the L-theanine you get from food. Supplements can also affect how some medications work. For more information, read the “What else do I need to know?” section below.

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What are the side effects?

Side effects have not been reported. But drinking too much tea may cause:

  • Headaches
  • Trouble staying asleep
  • Nausea (feeling like you’re going to throw up)
  • Irritability
  • Stomach pain
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What else do I need to know?

  • Talk with your healthcare provider if you’re taking medications that help you sleep such as lorazepam (Ativan®), diazepam (Valium®), or zolpidem (Ambien®). Taking these medications and L-theanine may increase drowsiness.
  • Talk with your healthcare provider if you’re pregnant or breastfeeding. L-theanine may not be safe for you.
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If you have questions or concerns, contact your healthcare provider. A member of your care team will answer Monday through Friday from to Outside those hours, you can leave a message or talk with another MSK provider. There is always a doctor or nurse on call. If you’re not sure how to reach your healthcare provider, call 212-639-2000.
If you have questions or concerns, contact your healthcare provider. A member of your care team will answer Monday through Friday from to Outside those hours, you can leave a message or talk with another MSK provider. There is always a doctor or nurse on call. If you’re not sure how to reach your healthcare provider, call 212-639-2000.

For more resources, visit www.mskcc.org/pe to search our virtual library.

L-Theanine - Last updated on November 22, 2022
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