L-Theanine in Tea and in Supplements: Green Tea Content and Extracts

How the evidence is labeled

Laboratory measurement means a chemical analysis of tea samples. Trial amount means what a study gave its volunteers, which is not advice. Insufficient evidence means there are too few studies to judge.

What a laboratory found in commercial teas

A laboratory study measured theanine and caffeine in commercial teas, using 1 gram of tea steeped in 100 ml of 80 °C water for 3 minutes. [1]

Points that matter when reading these numbers:

• Big variation. The authors found theanine content "rather variable" within each tea category and concluded that theanine and caffeine amounts do not reliably tell tea types apart. [1] A green tea is not guaranteed to have more theanine than a black tea.


• Brewing changes the result. In the paper, a 3-minute steep did not extract everything; a 90-minute extraction produced about twice as much theanine and 1.5 times as much caffeine in the liquid. [1] That is a laboratory finding, not a brewing recommendation.


• Caffeine comes along. In these samples every tea type had more caffeine than theanine by weight. [1] The FDA lists typical caffeine in a 12-ounce green tea at 37 milligrams. [2] Decaffeinated tea still contains some caffeine. [2] For other drinks see Caffeine in Coffee, Tea, Energy Drinks and Supplements.


• No decaf theanine figures. Proper evidence not found for theanine content of decaffeinated teas in the sources we read.


• Different units. The table is per gram of dry tea, not per cup. We do not convert it into cups because the amount of tea used and the steeping time change the result.

Tea in trials versus supplement trials

A 4-week matcha trial reported that its daily 2.7 grams of matcha contained 50.3 mg theanine, 301.4 mg catechins and 71.5 mg caffeine. [3] Measured sleep (EEG) did not differ from the control group. [3] By comparison, a stress review discussed supplement trials that used 200-400 mg a day of isolated L-theanine. [4] These are study amounts, not recommendations, and they show that tea-based and supplement-based trials are not testing the same exposure. A 2025 meta-analysis said more research was needed using tea beverages or tea-equivalent bioactive amounts. [5] Some of its authors work for tea companies. [5]

Supplements and extracts

• Isolated L-theanine (capsules, tablets, powders) is what most supplement trials used. See L-Theanine for Sleep, Stress and Anxiety.
• Green tea extracts contain catechins and often caffeine, and are a different product. The NCCIH reports side effects of green tea extract supplements include nausea, constipation, abdominal discomfort and increased blood pressure, and that liver injury has been reported, primarily with extracts in tablet or capsule form. [6] Green tea extract can also lower blood levels of a cholesterol medicine. [6] See Green Tea.
• Tea as a drink. The NCCIH says no safety concerns have been reported for green tea as a beverage for adults, noting it contains caffeine. [6] For black tea see Black Tea.
• Combined brain formulas often pair theanine with caffeine and other ingredients; see Caffeine Plus L-Theanine and Multicomponent "Brain" Formulas.

Reading a label

Packaged foods must list caffeine in the ingredients when it is added as a stand-alone ingredient, but many supplements state the amount only voluntarily. [2] If a label shows a blend, ask what each ingredient contributes. The FDA does not approve supplement safety or labeling before sale, according to a 2023 review. [7] See Quality Testing and Certifications.