L-theanine is an amino acid from tea leaves. It is used for calm, sleep and, together with caffeine, focus.
Calculator Official intake Study doses Best form Safety Sources
This is not an essential nutrient, so there is no official daily intake. Only study doses are shown.
These are doses tested in research, not personal advice. Some exceed the upper limit because they were short courses or given under medical care.
200-400 mg a day
A systematic review of 9 trials found 200 to 400 mg a day may reduce stress and anxiety in people under stressful conditions. The authors call for larger and longer studies.
200 mg a day
In 30 healthy adults, 200 mg a day for 4 weeks improved sleep scores, stress symptoms and some thinking tests. A 2025 meta-analysis of 18 trials found small improvements in falling asleep and overall sleep quality, but many trials mixed theanine with other ingredients.
97 mg as a single dose before the task or exercise
In 44 young adults, 97 mg L-theanine with 40 mg caffeine improved accuracy when switching tasks and made people feel more alert, but not other tests. A single dose before a demanding task.
No best form
Why: The trials used pure L-theanine; compare the mg on the label.
Green and black tea contain small amounts.
Few interactions are known. Ask your doctor if you take sedatives or blood pressure medicines.
Well tolerated in trials at a few hundred mg a day.
Pregnant, breastfeeding, on medication, or managing a health condition? Check with a doctor or pharmacist before starting a supplement.
Values checked: November 12, 2026.