L-Theanine, Relaxation and Sleep
Evidence-oriented guide to l-theanine, relaxation and sleep, including biological context, human research limits, safety and relevance to the Yu Sleep label.
Quick answer
L-theanine is an amino acid found in tea and has been studied for stress, relaxation and sleep-related outcomes.
What is it?
This ingredient is discussed here because it appears on the current Yu Sleep label. The purpose of this page is to explain the ingredient on its own terms, not to transfer study outcomes automatically to a finished multi-ingredient product.
What does the research tell us?
Human studies in sleep science often differ in population, dose, duration, outcome measures and product form. A useful interpretation asks whether the study population resembles the intended user, whether the dose is known, whether the trial was randomized and blinded, and whether the result was clinically meaningful rather than merely statistically significant.
What are the evidence limits?
Trials differ in dose and population. Because Yu Sleep does not disclose the L-theanine amount inside the blend, direct dose comparisons are not possible.
How does this relate to Yu Sleep?
Yu Sleep’s supplied Supplement Facts label confirms that this ingredient is present. For ingredients inside the 637 mg proprietary blend, the individual amount is not disclosed. Therefore this site does not claim the product contains the same dose used in any particular study.
Safety context
Dietary-supplement safety depends on dose, duration, medicines, medical conditions and individual response. People who take prescription drugs, are pregnant or nursing, or have a medical condition should discuss supplement use with a qualified healthcare professional.
Related reading
References
- Yu Sleep — current vendor sales page (pricing, package presentation, guarantee and vendor claims; checked September 2026).
- Yu Sleep refund policy (current 60-day policy and return instructions).
- Yu Sleep shipping policy (delivery and shipping information; wording should be rechecked at checkout because vendor pages contain inconsistent shipping-fee statements).
- NCCIH: Melatonin — What You Need to Know.
- NCCIH: Sleep Disorders and Complementary Health Approaches.
- NIH Office of Dietary Supplements: Dietary Supplement Fact Sheets.