L-Theanine
L-theanine is a non-protein amino acid that occurs naturally in the leaves of the tea plant, Camellia sinensis, and in a few other plants and fungi. Supplement-grade L-theanine is produced by enzymatic synthesis or extracted from green tea and supplied as a white crystalline powder.
How people respond to a stressor, and sleep quality, mostly at 200 mg a day: five placebo-controlled trials, a 2025 meta-analysis of eighteen studies, and a pharmacokinetic study. See the studies
On the label
Hypromellose (vegetarian capsule), rice flour.
As a dietary supplement, take one capsule with food whenever preferred. Do not consume more than four capsules per day.
The other two ingredients
Apart from the L-theanine, the capsule holds two things: rice flour and a cellulose shell. Both are food.
The shell is hypromellose, which is plant cellulose refined into a clear film. It keeps the powder dry until you swallow it, then dissolves in the stomach in a few minutes. No gelatin, so nothing from an animal, and no colouring.
Two hundred milligrams of L-theanine is a small pinch. On its own it would sit loose in a half-empty shell, and a half-empty capsule cannot be filled to a consistent weight. Rice flour makes up the difference. Each capsule is filled to the same weight, and that weight is how the dose is checked.
That is the full list. Nothing else goes in.
What the bottle does
The bottle is amber PET. It is what the pharmaceutical industry uses for tablets and capsules because, of the common bottle plastics, it lets the least oxygen through. It has no BPA and no phthalates in it. It does not break like glass and weighs much less, so shipping it takes less fuel. It is also the most recycled plastic there is, the number one inside the triangle on the base.
Light, air and moisture are what age a capsule. The amber tint blocks the ultraviolet. A tear-resistant seal under the cap keeps air and moisture out until you break it.
A band around the neck shows the bottle has not been opened since it was filled. A cotton insert stops the capsules rattling and breaking in the post. The lot number and date on the base link the bottle to its certificate.
Keep it somewhere cool, dry and dark.
Questions about L-Theanine
Why 200 mg?
Most controlled trials of L-theanine on its own gave 200 mg as a single dose, so that is the capsule. The studies are listed below as published.
Is it the same as the theanine in tea?
Yes, the same molecule. A cup of green tea holds somewhere in the tens of milligrams depending on the leaf and the brew, so one capsule is several cups' worth.
How do I get the certificate for my lot?
Email the lot number printed on the base of your bottle to support@symnutrition.com and we will send the certificate of analysis for that lot within two business days.
The studies
These are some of the studies that convinced us this was a product worth making. There is an inherent bias in the interaction between a brand and its customer, so we do not summarise them for you. Each is listed as published with its design, size and dose, including the ones with mixed or null results, and the link goes to the paper. Read them, and do your own research using unbiased and reputable sources.
-
Hidese S et al. (2019). Nutrients. Randomised, double-blind, placebo-controlled crossover, n = 30, 200 mg/day for 4 weeks.
-
L-Theanine reduces psychological and physiological stress responses
Kimura K et al. (2007). Biological Psychology. Double-blind, placebo-controlled crossover, n = 12, 200 mg single dose.
-
Evans M et al. (2021). Neurology and Therapy. Randomised, triple-blind, placebo-controlled crossover, n = 16, 200 mg single dose.
-
Sarris J et al. (2019). Journal of Psychiatric Research. Randomised, double-blind, placebo-controlled, n = 46, 450 to 900 mg/day for 8 weeks.
-
The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis
Bulman A et al. (2025). Sleep Medicine Reviews. Systematic review and meta-analysis of 18 studies, n = 897, doses varied.
-
Scheid L et al. (2012). Journal of Nutrition. Randomised crossover, pharmacokinetics, n = 12, 50, 100 and 200 mg single doses.
L-Theanine 200mg per capsule, 150 vegetable capsules
Six-month refund. If anything is not right, email your Amazon order ID and we will sort it out. No questions.