L-theanine dosage: how much per day and when to take it

Short answer: There is no official recommended daily amount of L-theanine. In studies, adults usually took 100 to 400 mg a day, often 200 mg, for no longer than 8 weeks in a row. Our capsule label says: 1 capsule (196 mg L-theanine), once or twice a day, preferably with or just after a meal.

Last updated: 6 November 2026 · Written by Florian Fermin

Below I go through what the label says, which L-theanine dosages were used in research, how fast L-theanine reaches your blood and how to do the maths for capsules, tea and matcha. What L-theanine is and what research says about it, you can read in L-theanine effects: what research says about dosage and use.

We at GOYU sell L-theanine capsules ourselves. No health claims have been approved for L-theanine in the EU: EFSA found that a cause and effect relationship with the proposed effects had not been established (EFSA, 2011). So study results say nothing about what a product will do for you.

How much L-theanine per day?

Follow the label of your product and do not take more. Unlike vitamins, L-theanine has no official daily reference amount. As a guide:

The 196 to 392 mg in our L-theanine capsules falls within what studies used. Taking less is always fine. Personally I would stick to 1 capsule a day for the first week; that is my own advice, not a rule from the label.

How many mg of L-theanine are in a capsule?

Count the milligrams of L-theanine, not the weight of the extract. Many labels list an extract with a percentage. This is how you convert it:

1. Find the weight of extract per capsule: in our case 200 mg green tea extract.
2. Multiply by the L-theanine percentage: 200 mg x 98% = 196 mg L-theanine.
3. Multiply by the number of capsules per day: 1 to 2 capsules is 196 to 392 mg.
4. Divide the number of capsules by the number per day: 60 capsules last 30 to 60 days.

If a label only says "L-theanine 200 mg", that is usually the amount of L-theanine itself. Then check the source as well. Why that matters is explained below.

Which dosages were used in research?

Most studies gave 100 to 400 mg L-theanine, as a single dose or every day for a few weeks. A few examples, with what was given and to whom:

• A systematic review of 9 randomised studies found amounts of 200 to 400 mg a day, in studies lasting up to 8 weeks (Williams et al., 2020).
• In a Japanese study, 30 healthy adults aged 20 to 69 took 200 mg every evening before bed for 4 weeks, and a placebo for another 4 weeks (Hidese et al., 2019). Two of the authors work for an L-theanine manufacturer.
• In studies on attention, participants often got a single dose of 100 to 200 mg, sometimes together with 50 to 250 mg caffeine (Owen et al., 2008; Rogers et al., 2008).
• A 2026 meta-analysis pooled 31 randomised studies with 1,168 participants in total. A common set-up was a single 200 mg dose, 30 to 60 minutes before testing (Gerolymos et al., 2026).

I deliberately leave out what those studies found: they were mostly small and short, and without an approved claim we do not link any effect to L-theanine. Also note: part of the research used L-theanine made with enzymes. According to the European Commission's Novel Food Catalogue, L-theanine extracted and isolated from green tea is not a novel food in food supplements; L-theanine from other sources is.

When should you take L-theanine?

Take our capsules with water, preferably with or just after a meal. That is what the label says, and the pack also says not to take them on an empty stomach. There is no proven best time of day: in studies it depended on what was being researched.

• During the day: in studies on attention, people took L-theanine during the day, often with caffeine, and measurements were taken 30 to 90 minutes later.
• In the evening: in the 4-week Japanese study, participants took it before bed.
• 2 capsules a day: the label says 1 capsule, once or twice a day. So take the second capsule with a different meal, for example breakfast and lunch.

How fast does L-theanine work and how long does it stay in your blood?

L-theanine is absorbed quickly: after about 50 minutes the level in your blood is highest, after which it halves in about an hour. Whether and when you notice anything, we cannot say: the level in your blood does not tell you what you feel.

• In a study of 12 healthy adults, blood levels peaked 0.8 hours after 100 mg L-theanine. Capsules and green tea with the same amount gave comparable values (Scheid et al., 2012).
• With 25 to 100 mg L-theanine, from tea or dissolved in water, it appeared in the blood after about 10 minutes, peaked after about 50 minutes and had a half-life of about 65 minutes (van der Pijl et al., 2010).
• Studies on attention and mood mainly measured in the first and second hour after intake (Payne et al., 2025).

L-theanine and caffeine: how much together?

In research, L-theanine was often combined with caffeine, for example 100 mg L-theanine with 50 mg caffeine (Owen et al., 2008) or 200 mg with 250 mg (Rogers et al., 2008). With a combination like that, keep an eye on your caffeine above all. The European Food Safety Authority (EFSA) sees no safety concern for healthy adults up to 400 mg caffeine a day from all sources combined, and up to 200 mg at once. For pregnant women, EFSA gives 200 mg a day (EFSA, 2015).

Important for our capsules: the pack says not to use them on a day when you also take other products containing green tea. That warning applies to green tea extract (Regulation (EU) 2022/2340). So do not combine our capsules with matcha or green tea on the same day. Coffee does not fall under this. What else is known about side effects and interactions is covered in L-theanine side effects.

How much L-theanine do you get from tea or matcha?

Tea gives you much less than a capsule. In one analysis, a 200 ml cup of tea brewed for 2 minutes contained on average 8 mg (green tea) to 24 mg (black tea) L-theanine (Keenan et al., 2011). Matcha contains more because you drink the whole leaf: in a Japanese study, 2.7 grams of matcha contained 50.3 mg L-theanine and 71.5 mg caffeine (Baba et al., 2024).

To reach 200 mg through tea, those averages mean 8 to 25 cups, with all the caffeine that comes with them. The figures per type of tea and per cup are in L-theanine in green tea, matcha and other foods. Our matcha is at buy matcha.

Summary in 3 points

• There is no official daily amount of L-theanine. In studies, adults usually took 100 to 400 mg a day, for up to 8 weeks in a row.
• Our label says 1 capsule of 196 mg L-theanine, once or twice a day, with or just after a meal and not on an empty stomach.
• L-theanine peaks in your blood after about 50 minutes and halves in about an hour. Do not use our capsules on the same day as matcha or other products containing green tea.

Frequently asked questions

How many mg of L-theanine per day?

In studies, adults usually took 100 to 400 mg a day, often 200 mg. There is no official recommended amount. According to our label you take 1 capsule, once or twice a day: 196 to 392 mg L-theanine.

When should you take L-theanine?

Our label says: with water, preferably with or just after a meal, and not on an empty stomach. There is no proven best time. Studies on attention gave it during the day; one 4-week study gave it before bed.

How fast does L-theanine work?

L-theanine is measurable in your blood after about 10 minutes and peaks after about 50 minutes. Studies usually measured 30 to 90 minutes after intake. Whether you notice anything differs from person to person, and we cannot promise it.

How long does L-theanine last?

Whether and for how long you notice anything has not been studied well. What is known is how long it stays in your blood: the half-life is about 65 minutes, so after just over an hour half of the peak is gone. In studies, L-theanine was taken daily for up to 8 weeks; little is known about longer use.

Sources

1. EFSA NDA Panel (2011). Scientific Opinion on the substantiation of health claims related to L-theanine from Camellia sinensis (L.) Kuntze (tea). EFSA Journal 9(6):2238. doi:10.2903/j.efsa.2011.2238
2. Williams JL, Everett JM, D'Cunha NM, et al. (2020). Plant Foods for Human Nutrition 75(1):12-23. Systematic review of 9 randomised studies. PubMed 31758301
3. Hidese S, Ogawa S, Ota M, et al. (2019). Nutrients 11(10):2362. Randomised, double-blind, crossover, 30 adults, 4 weeks; two authors work for an L-theanine manufacturer. doi:10.3390/nu11102362
4. Owen GN, Parnell H, De Bruin EA, Rycroft JA (2008). Nutritional Neuroscience 11(4):193-198. 27 participants, single dose. doi:10.1179/147683008X301513
5. Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW (2008). Psychopharmacology 195(4):569-577. 48 participants, single dose. doi:10.1007/s00213-007-0938-1
6. Gerolymos C, Saddier E, Boyer L, Fond G (2026). Molecular Psychiatry 31(11):6592-6602. Meta-analysis of 31 randomised studies. doi:10.1038/s41380-026-03727-9
7. Scheid L, Ellinger S, Alteheld B, et al. (2012). Journal of Nutrition 142(12):2091-2096. Crossover, 12 participants, capsules and green tea. doi:10.3945/jn.112.166371
8. van der Pijl PC, Chen L, Mulder TPJ (2010). Journal of Functional Foods 2(4):239-244. Uptake of 25 to 100 mg L-theanine. doi:10.1016/j.jff.2010.08.001
9. Payne ER, Aceves-Martins M, Dubost J, Greyling A, de Roos B (2025). Nutrition Reviews 83(10):1873-1891. Meta-analysis; two authors work for a tea company. doi:10.1093/nutrit/nuaf054
10. EFSA NDA Panel (2015). Scientific Opinion on the safety of caffeine. EFSA Journal 13(5):4102. doi:10.2903/j.efsa.2015.4102
11. Keenan EK, Finnie MDA, Jones PS, Rogers PJ, Priestley CM (2011). Food Chemistry 125(2):588-594. Analysis of tea bags and loose tea. doi:10.1016/j.foodchem.2010.08.071
12. Baba Y, Takihara T, Okamura N (2024). Nutrients 16(17):2907. doi:10.3390/nu16172907
13. Commission Regulation (EU) 2022/2340 on green tea extracts containing (-)-epigallocatechin-3-gallate. eur-lex.europa.eu
14. European Commission, Novel Food Catalogue, entry L-theanine (POL-NF-00443, consulted November 2026): L-theanine extracted and isolated from green tea is not a novel food in food supplements, and only there; L-theanine from other sources is a novel food. food.ec.europa.eu
15. GOYU, label and product page Green Tea Extract Capsules 200 mg (L-Theanine), consulted 6 November 2026.

More products related to focus and concentration, such as matcha and ginkgo, are at supplements for focus and concentration. Our L-theanine capsules are not listed there, because no claim has been approved for L-theanine.

This article is for information only and is not medical advice. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, pregnant or taking medication, talk to your doctor or pharmacist.