The Effect of the Amino Acid L-Theanine on Alertness and Vigilance

Status

Completed

Phases

Study type

Interventional

Source

ClinicalTrials.gov

Registry ID

NCT01851122

Enrollment

Registered

2013-05-10

Start date

2011-11-30

Completion date

2012-10-31

Last updated

2023-12-13

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

Theanine, (L)-Isomer

Keywords

l-theanine, alertness, well-being

Brief summary

The amino acid l-theanine (the active ingredient in green tea) is considered to have a calming effect without causing sleepiness. This study evaluates whether l-theanine affects blood pressure, heart rate, alertness, and sense of well-being.

Interventions

DIETARY_SUPPLEMENTL-theanine capsule

L-theanine 250mg capsule

DIETARY_SUPPLEMENTPlacebo capsule

Study design

Allocation

RANDOMIZED

Intervention model

CROSSOVER

Primary purpose

TREATMENT

Masking

DOUBLE (Subject, Investigator)

Eligibility

Sex/Gender

ALL

Age

18 Years to No maximum

Healthy volunteers

Yes

Inclusion criteria

* adult * able to swallow capsule

Exclusion criteria

* none

Design outcomes

Primary

Measure	Time frame	Description
Alertness	48 hrs	The average response time to identify a small rectangle shown on a computer screen.
Well-Being	48 hrs	Sense of subjective well-being as measured on a visual analog scale

Countries

United States

Outcome results

None listed

Source: ClinicalTrials.gov · Data processed: Feb 4, 2026