What it is
L-theanine is an amino acid found almost exclusively in tea (Camellia sinensis), close to glutamate and glutamine in structure. It is not an essential nutrient and has no recommended intake. People buy it for stress, for concentration, often paired with caffeine, and for sleep.
What the label does not say
- The Canadian monograph allows 200 to 250 mg per day for the claim "helps to temporarily promote relaxation"; the 2020 systematic review (9 trials) covers 200 to 400 mg per day. A 200 mg capsule is therefore worth about 8 cups of black tea or 25 of green tea, without the caffeine that tea brings along with it.
- In Canada, a product that contains caffeine, from any source, cannot carry any relaxation or sedation claim. A "calm and focus" product that combines theanine and caffeine can therefore promise only alertness on its licensed label.
- In the meta-analysis of acute effects (11 trials), the caffeine and theanine combination improves alertness and attention-switching accuracy during the 2 hours after the dose, and the size of the effect tracks the caffeine dose more than the theanine dose. The "focus" being sold is mostly the caffeine's.
- On sleep, the data are subjective: in 30 healthy adults, 200 mg per day for 4 weeks improved PSQI questionnaire sub-scores (latency, disturbances, use of a sleep aid) compared with placebo, without polysomnography. Examine writes that it is not known whether it helps insomnia in general.
The forms on the shelf
- L-theanine isolated from tea leaf or synthetic: the two sources accepted by the Health Canada monograph, which requires a purity of at least 98% L-theanine, measured by a method that separates the L form from the D form.
- Theanine and caffeine: the most studied combination, often 200 mg of each in the trials cited by Examine, for alertness and attention rather than for calm.
- Tea: a 200 mL cup provides on average 24 mg for black tea and 8 mg for green tea, with steeping time being the main determinant.
Published reference values
- No recommended intake or upper limit. Canadian benchmark: 200 to 250 mg per day for adults, with no required warning or maximum duration. Trials on stress and anxiety: 200 to 400 mg per day, with possible help in stressful situations and a call for longer and larger trials.
- Adverse effects: Health Canada requires no statement. Examine points to sparse data suggesting reduced alertness, consistent with the intended effect, and a slight antagonist effect on caffeine, still to be confirmed.
When
The acute trials measure the effect within 2 hours of the dose; the stress and sleep trials gave it every day for 4 weeks or more. With caffeine, the intended effect is daytime concentration, not sleep.
To mention to a professional
- Pregnancy and breastfeeding: no data in the sources consulted. Use of a sedative, a prescribed stimulant or a blood pressure medication: check with a health care professional.
What it is sold for, and what the data show
L-theanine is sold for calm without drowsiness and for better sleep. The actual data amount to a handful of small trials with subjective measures, at 200 to 400 mg per day; the concentration side depends mostly on the caffeine that goes with it, and nothing establishes an effect on insomnia. The risk is low; the gap is between the promise and the size of the trials.
From the plate first
Tea, and just about nothing else: 24 mg per 200 mL cup of black tea on average, 8 mg for green tea, more with a long steep, less with a lot of milk.
Sources
- Health Canada, natural health product monograph, L-Theanine
- Health Canada, monograph, Cognitive Function Products (rule on caffeine and relaxation claims)
- Williams et al., L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review, Plant Foods for Human Nutrition, 2020
- Camfield et al., Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis, Nutrition Reviews, 2014
- Hidese et al., Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults, Nutrients, 2019
- Keenan et al., How much theanine in a cup of tea? Effects of tea type and method of preparation, Food Chemistry, 2011
- Examine.com, Theanine
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.