Health functional food ingredient
L-theanine review — stress-related tension and the evidence
Also known as: theanine, L-theanine supplement
At a glanceL-theanine, an amino acid in tea, may help relieve stress-related tension at 200–250 mg a day per Korea's MFDS. Evidence comes mainly from small studies.
| Effect examined | Evidence | What studies found |
|---|---|---|
| Stress-related tension | Limited evidence | In a small 2019 randomized controlled trial in healthy adults, those who took 200 mg a day for four weeks had better scores on stress-related symptoms than the placebo group. Larger studies are needed. |
What it is
L-theanine is an amino acid found in the leaves of the tea plant used for green and black tea. In Korea it is listed as a health functional food ingredient under the name theanine.
What the MFDS recognizes
Korea’s official notice says theanine “may help relieve tension caused by stress” at 200–250 mg of L-theanine a day. This does not mean it treats anxiety or insomnia as medical conditions.
What studies show
In 2019 a research team in Japan gave healthy adults 200 mg of L-theanine or placebo daily for four weeks. Stress-related symptom scores improved more in the theanine group, but the study was small, and larger trials are needed before drawing broad conclusions.
Theanine and caffeine
Tea leaves contain both theanine and caffeine, yet the official notice separately advises care when taking theanine supplements with caffeinated drinks such as coffee, black tea and green tea. Caffeine is covered in our caffeine review.
Good to know
- The official notice advises care when combining it with caffeinated drinks such as coffee, black tea and green tea.
- If you are pregnant, breastfeeding or facing surgery, talk to a professional before taking it.
This review does not recommend any product. If you take medication, are pregnant or breastfeeding, or have a health condition, talk to a doctor or pharmacist first.
References
- MFDS Notice No. 2026-43, Standards and Specifications for Health Functional Foods (Korean). Section 2-54, theanine
- Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Hidese S et al. Nutrients 11, 2362 (2019)