L-Theanine Explained: The Amino Acid Found in Tea Leaves

By the Zespo team · Updated 26 October 2026

L-theanine is an amino acid found almost only in the tea plant (Camellia sinensis) and in one species of mushroom. It was first identified in green tea leaves in Japan in 1949.

How much is in a cup of tea?

Amounts vary by tea type and brewing, but a cup of green or black tea typically contains somewhere around 8 to 30 mg of L-theanine. Shade-grown teas such as matcha and gyokuro tend to contain more.

How is it made for supplements?

Supplement-grade L-theanine is usually produced by fermentation or enzymatic synthesis, which yields the pure L-form found in tea. Labels list it in milligrams per serving, commonly 100 to 250 mg.

What to check before you buy

• The amount of each ingredient per serving, not just per capsule
• How many capsules make one serving and how many servings are in the pack
• Whether any ingredient sits inside an undisclosed "proprietary blend"
• An FSSAI licence number and the veg/non-veg mark on the pack

Label facts: Zespo L-Theanine 200 mg - 90 Veg Capsules

• 200 mg per capsule - the standard serving used in research
• The amino acid naturally present in green tea, without the caffeine
• Single ingredient, 90-day supply
• Made in India in a GMP-certified facility, FSSAI-licensed

See Zespo L-Theanine 200 mg - 90 Veg Capsules on zespo.in · Also on Amazon.in (search "Zespo").

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Zespo products are food supplements, not medicines. This article is for general information and is not medical advice. Take supplements as directed on the label and speak to a qualified healthcare professional if you are pregnant, nursing, taking medication or have a medical condition.