What Happens When You Drink Green Tea With L-Theanine

Posted by AweSamo January 8, 2026
What Happens When You Drink Green Tea With L-Theanine

Key Takeaways

  • Green tea is a good source of caffeine and L-theanine, containing both in moderate amounts.
  • The combination of green tea and L-theanine creates a calm alertness that supports mental clarity while reducing jitteriness.
  • Consuming too much of either caffeine or L-theanine can lead to unwanted side effects, so it’s important to drink green tea in moderation.

Green tea contains caffeine, which can promote wakefulness and alertness. It also contains the amino acid L-theanine, which leads to feelings of relaxation and calm. When you consume green tea with L-theanine, it provides both calm and alertness, creating wakefulness without feeling wired.

Caffeine and L-Theanine Content in Green Tea

Green tea is made using the leaves of the Camellia sinensis plant. This plant is used to make all true teas, each with a different processing method. The processing of green tea is minimal, consisting only of steaming and pan-frying, as opposed to fermentation, as in black and oolong teas.

L-theanine is a naturally occurring amino acid found in the leaves of tea. When in contact with water, it dissolves and imparts flavor. When consumed, L-theanine affects neurotransmitters in the brain, leading to feelings of relaxation and stress reduction.

One serving of green tea contains roughly 25-60 milligrams (mg) of L-theanine and approximately 30-40 mg of caffeine.

How Much Caffeine and L-Theanine Can I Have Per Day?

The generally considered safe limit of caffeine is 400 mg per day for adults, whereas the upper limit of L-theanine may depend on why a person is taking it. There are clinical studies in adults that have used approximately 100-400 mg of L-theanine daily for up to 8 weeks.

The Effects of L-Theanine in Green Tea

When you drink green tea with L-theanine, you can get the benefits of caffeine and the amino acid. Caffeine tends to promote alertness and an increased sense of overall well-being. It can also:

  • Improve mood
  • Increase concentration
  • Minimize feelings of depression 

L-theanine, on the other hand, promotes feelings of calm and relaxation. However, it can also help in a similar way to caffeine, improving mood, concentration, and overall well-being. L-thenine also reduces feelings of stress while minimizing anxiety symptoms.

When you drink green tea and get both caffeine and L-theanine, you may experience feelings of calm and alert focus, with a more subtle lift in mental energy without the wired or jittery feelings that may occur when drinking caffeinated beverages without L-theanine.

Working Together

Caffeine and L-theanine don’t cancel each other out when consumed in green tea. Instead, they may work together to provide a steady boost in mental energy while maintaining calm and reducing stress.

What About Supplements?

While green tea and L-theanine work together to confer benefits, there is little scientific evidence to determine whether taking green tea extract with L-theanine supplements produces the same effect.

Potential Risks and Considerations

It’s also important to consider the potential downsides of consuming both caffeine and L-theanine. For example, consuming too much caffeine can lead to:

  • Increased heart rate
  • Heart palpitations
  • High blood pressure
  • Inability to sleep
  • Anxiety and jitters
  • Upset stomach

You can also take too much L-theanine, which can lead to side effects such as:

  • Nausea
  • Abdominal pain
  • Headaches
  • Irritability
  • Diarrhea
  • Constipation
  • Loss of appetite

These side effects are typically mild.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Radeva-Ilieva M, Stoeva S, Hvarchanova N, Georgiev KD. Green tea: Current knowledge and issues. Foods. 2025;14(5):745. doi:10.3390/foods14050745

  2. National Center for Complementary and Integrative Health. Green tea.

  3. Sleep Foundation. L-theanine for sleep.

  4. Jówko E. Green tea catechins and sport performance. In: Lamprecht M, ed. Antioxidants in Sport Nutrition. Boca Raton (FL): CRC Press/Taylor & Francis; 2015.

  5. U.S. Food and Drug Administration. Spilling the beans: How much caffeine is too much?

  6. U.S. Food and Drug Administration. FDA briefing document: L-theanine.

  7. Williams JL, Everett JM, D’Cunha NM, et al. The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: A systematic review. Plant Foods Hum Nutr. 2020. 75, 12–23. doi:10.1007/s11130-019-00771-5

  8. Nehlig A. Effects of coffee/caffeine on brain health and disease: What should I tell my patients?. Pract Neurol. 2016;16(2):89-95. doi:10.1136/practneurol-2015-001162

  9. Williams JL, Everett JM, D’Cunha NM, et al. The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: A systematic review. Plant Foods Hum Nutr. 2020;75(1):12-23. doi:10.1007/s11130-019-00771-5

  10. Kahathuduwa CN, Wakefield S, West BD, et al. Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: A proof-of-concept neuroimaging RCT. Sci Rep. 2020;10(1):13072. doi:10.1038/s41598-020-70037-7

  11. Moshfeghinia R, Sanaei E, Mostafavi S, Assadian K, Sanaei A, Ayano G. The effects of L-theanine supplementation on the outcomes of patients with mental disorders: A systematic review. BMC Psychiatry. 2024;24(1):886. doi:10.1186/s12888-024-06285-y

Angelica Bottaro

By Angelica Bottaro

Bottaro has a Bachelor of Science in Psychology and an Advanced Diploma in Journalism. She is based in Canada.

Tags: