Improvement after a supplement is not the same as a comparative result
Start with the comparison. A before-and-after change alone cannot isolate the contribution of an ingredient.
L-Theanine
Selected research topic
Stress and mood
Findings differ across measurements or study conditions. The results below keep them separate.
Some findings concern patients or people with a deficiency.
- Publications for this topic
- 17
- Human comparison publications
- 2
- Publications needing review
- 14
Findings in the studies
HDRS
Publications linked to this measurement: 1
- A better result than the comparison group was reported.Patient group · Separable contribution
Measurement and study conditions
- Study type
- Randomized controlled trial: subjects were randomly assigned to groups for comparison.
- Study population
- Human participants · Patient group
- Ingredients tested
- Separable contribution
- How results were compared
- Results were compared between groups. · Study comparison: Sertraline plus L-theanine versus sertraline plus matched placebo; adjunct effect on HDRS during tre
- Additional measurement information
- Secondary outcome
- Measurement time
- Weeks 2, 4, and 6; six-week trial
markers of stress
Publications linked to this measurement: 1
- No clear difference from the comparison group was found.General population · Separable contribution
Measurement and study conditions
- Study type
- Randomized controlled trial: subjects were randomly assigned to groups for comparison.
- Study population
- Human participants · General population
- Ingredients tested
- Separable contribution
- How results were compared
- Results were compared between groups. · Study comparison: L-theanine arm versus placebo on markers of stress during the mental stress challenge
- Additional measurement information
- Biomarker
- Measurement time
- Before and after the mental stress challenge
HAMD-21 score
Publications linked to this measurement: 1
Other human research, including observational studies and reviews
- A change was reported before and after use. Its cause cannot be isolated.Patient group · Separable contribution · 8 weeks
Measurement and study conditions
- Study type
- Clinical trial
- Study population
- Human participants · Patient group
- Ingredients tested
- Separable contribution
- How results were compared
- Changes within the same group were compared. · Study comparison: Open-label within-patient HAMD-21 pre/post change after add-on l-theanine
- Additional measurement information
- Primary outcome
- Measurement time
- 8 weeks
This result is held for interpretation. That does not mean research found no effect.
Outcome groups needing additional review (9)
- anti-stress effects · Distinct papers needing additional review: 1Direction unclear: 1
- anxiolytic and calming effect · Distinct papers needing additional review: 1Evidence criteria check: 1
- DASS-42 stress score · Distinct papers needing additional review: 1Evidence criteria check: 1
- depression · Distinct papers needing additional review: 1Evidence criteria check: 1
- depressive-like behaviors · Distinct papers needing additional review: 1Evidence criteria check: 1
- overall mood · Distinct papers needing additional review: 1Direction unclear: 1
- state anxiety · Distinct papers needing additional review: 1Evidence criteria check: 1
- subjective stress response to a multitasking cognitive stressor · Distinct papers needing additional review: 1Evidence criteria check: 1
- Tension-Anxiety scores · Distinct papers needing additional review: 1Evidence criteria check: 1
One paper can appear under multiple measured outcomes or review reasons, so these counts should not be added together.
Representative outcome and study details
Human studies reported a within-group change in HAMD-21 score.
Human studies · Includes patient groups · within-group comparison
1 publications linked to this result
- Route, form, dose, or population details are incomplete, so the findings cannot be confirmed as directly comparable.
Data coverage and detailed study classifications
Paper counts are separated by research topic below. One paper may contribute to multiple findings.
Analysis status: Public-ready
Ingredient analysis date:
How the grade was determined: C
The 9.4 evidence score includes 3 independent human studies and 3 clinical studies in the representative benefit area. The C tier remains conservative because of limited repetition across independent human clinical studies.
The grade is based mainly on the research area with the most evidence. It does not mean the same result was found in other areas.
Papers linked to this ingredient overall: 97
Papers linked to this topic 17 · distinct papers 17 · papers with a confirmed human comparison 2 · papers needing additional review 14
A publication may appear in more than one count. These numbers should not be added. Ingredient-wide papers, topic-linked papers, and sources in outcome groups use different scopes. Adding source counts may count the same paper more than once.
- anti-stress effects: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- anxiolytic and calming effect: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- DASS-42 stress score: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- depression: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- depressive-like behaviors: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- HAMD-21 score: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- HDRS: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 1
- markers of stress: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 1
- overall mood: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- state anxiety: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- subjective stress response to a multitasking cognitive stressor: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- Tension-Anxiety scores: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
What the research found
markers of stress
No clear difference in this measurement was found between the compared groups.
Controlled study in people · Separable contribution · General population
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
HDRS
The study reported improvement in this measurement.
Controlled study in people · Separable contribution · Patient group
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
HAMD-21 score
A change was reported before and after use. Its cause cannot be isolated.
Other evidence · Separable contribution · Patient group
Within-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
anti-stress effects
The study needs further checking before its result can be interpreted.
Review · Ingredient combination · Unspecified population
Several ingredients were used together. This does not establish the effect of this ingredient alone or synergy.
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
anxiolytic and calming effect
The study needs further checking before its result can be interpreted.
Review · Unknown intervention · General population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
DASS-42 stress score
The study needs further checking before its result can be interpreted.
Controlled study in people · Ingredient combination · General population
Several ingredients were used together. This does not establish the effect of this ingredient alone or synergy.
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
depression
The study needs further checking before its result can be interpreted.
Review · Unknown intervention · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
depressive-like behaviors
The study needs further checking before its result can be interpreted.
Animal study · indirect · Single ingredient · Patient group
This finding comes from animal or cell research. It does not establish the same effect in people.
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
overall mood
The study needs further checking before its result can be interpreted.
Meta-analysis · Ingredient combination · General population
Several ingredients were used together. This does not establish the effect of this ingredient alone or synergy.
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
state anxiety
The study needs further checking before its result can be interpreted.
Controlled study in people · Ingredient combination · General population
Several ingredients were used together. This does not establish the effect of this ingredient alone or synergy.
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
subjective stress response to a multitasking cognitive stressor
The study needs further checking before its result can be interpreted.
Controlled study in people · Ingredient combination · General population
Several ingredients were used together. This does not establish the effect of this ingredient alone or synergy.
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Tension-Anxiety scores
The study needs further checking before its result can be interpreted.
Controlled study in people · Single ingredient · General population
Within-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Review · Single ingredient · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
2 papers · 2 measured outcomes
2 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Review · Single ingredient · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Other evidence · Unknown intervention · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Other evidence · Unknown intervention · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Review · Unknown intervention · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
How to read research findings
How should I read research findings?
Research guidesNo clear difference and an uninterpretable result are different
A reported null comparison contains a result. An abstract without an interpretable comparison leaves a question unresolved.
Paper counts and study counts are different
Count original research separately from research that reanalyzes it. Publication volume is neither replication nor a quality rating.
Side effects and combination findings
Findings from this ingredient alone are shown separately from those involving another supplement or medication.
No combination cautions are available to show in the current data. This does not guarantee safety.
Review 1 combination findings and 0 findings that outperformed an ingredient alone.
Reported improvements with combinations
Combination findings are grouped by how the study compared them. This is not a recommendation to combine ingredients.
Combinations with reported improvement
The combination showed improvement, but each ingredient's contribution is unclear.
CaffeineL-theanine combined with caffeine significantly reduced caffeine-induced tachycardia (17% vs 92%) and state anxiety compared to caffeine alone.