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GABA and perceived stress: grade C

Limited evidence. Direction: No effect.

C LimitedIndustry-fundedShort-term only

Educational guidance, not medical advice

Why this grade

Rubric condition met: Small single-dose studies measuring mostly physiological markers; self-reported stress did not change consistently

The 2020 systematic review found limited evidence for stress, and a 2015 review noted that most evidence for a calming effect came from researchers with a potential conflict of interest. Most trials were single-dose studies measuring brain waves, heart rate variability or salivary markers, several run by researchers employed by Pharma Foods International, Ezaki Glico or Coca-Cola (Japan). In the largest, a single-blind crossover in 63 adults with four authors from Pharma Foods International, 100 mg reduced the stress-related fall in EEG activity; the authors reported that mood scores matched, but the 2020 review found participants did not report feeling more relaxed or less tense. Self-reported stress therefore has limited, mixed support, and the proposal is C with direction none.

How we grade evidence

Studies this grade rests on

EffectMixedNo effectSize shows participants (n)20052010201520202025Meta-analysisCrossover RCTNarrative reviewYoto 2012, 2012: crossover RCT, n = 63, result not recordedKanehira 2011, 2011: crossover RCT, n = 30, result not recordedAbdou 2006, 2006: crossover RCT, n = 21, result not recordedNakamura 2009, 2009: crossover RCT, n not recorded, result not recordedBoonstra 2015, 2015: narrative review, n not recorded, result not recordedHepsomali 2020, 2020: meta-analysis, n not recorded, result not recorded
each study this grade rests on, by publication year and design. Solid: effect versus the comparator; half-filled: mixed; hollow: no effect; dashed: result not recorded yet. Larger marks had more participants.
Show the numbers
StudyYearDesignParticipantsResult
Abdou 20062006crossover RCT21result not recorded
Nakamura 20092009crossover RCTnot recordedresult not recorded
Kanehira 20112011crossover RCT30result not recorded
Yoto 20122012crossover RCT63result not recorded
Boonstra 20152015narrative reviewnot recordedresult not recorded
Hepsomali 20202020meta-analysisnot recordedresult not recorded

Relieving occupational fatigue by consumption of a beverage containing γ-amino butyric acid.

Kanehira T, Nakamura Y, Nakamura K. Relieving occupational fatigue by consumption of a beverage containing γ-amino butyric acid J Nutr Sci Vitaminol (Tokyo), 2011. PMID 21512285

Result not recorded
Design
Controlled single-dose trial (single-blind crossover per S1)
Sample
n = 30
Population
Healthy adults, 9 with chronic fatigue
Funding
not stated in the PubMed or Crossref record; authors affiliated with Coca-Cola (Japan) Co., Ltd. and Pharma Foods International Co., Ltd. (J-STAGE article page, checked 2026-11-12)

Psychological stress-reducing effect of chocolate enriched with gamma-aminobutyric acid (GABA) in humans: assessment of stress using heart rate variability and salivary chromogranin A.

Nakamura H, Takishima T, Kometani T. Psychological stress-reducing effect of chocolate enriched with gamma-aminobutyric acid (GABA) in humans: assessment of stress using heart rate variability and salivary chromogranin A Int J Food Sci Nutr, 2009. PMID 19462324

Result not recorded
Design
Randomized controlled crossover experiments
Population
Healthy men under an arithmetic stress task
Funding
not stated in the PubMed or Crossref record; authors affiliated with Ezaki Glico Co. Ltd.

Oral intake of γ-aminobutyric acid affects mood and activities of central nervous system during stressed condition induced by mental tasks.

Yoto A, Murao S, Motoki M. Oral intake of γ-aminobutyric acid affects mood and activities of central nervous system during stressed condition induced by mental tasks Amino Acids, 2012. PMID 22203366

Result not recorded
Design
Randomized, single-blind, placebo-controlled crossover trial
Sample
n = 63
Population
Healthy adults under a mental-task stress condition
Funding
not stated in the PubMed or Crossref record; four of nine authors affiliated with Pharma Foods International Co. Ltd and one with Mitsubishi Corporation (publisher affiliation strings via OpenAlex, checked 2026-11-12)

Relaxation and immunity enhancement effects of gamma-aminobutyric acid (GABA) administration in humans.

Abdou AM, Higashiguchi S, Horie K. Relaxation and immunity enhancement effects of gamma-aminobutyric acid (GABA) administration in humans Biofactors, 2006. PMID 16971751

Result not recorded
Design
Two small controlled experiments (crossover EEG study; parallel bridge-crossing study)
Sample
n = 21
Population
Healthy adults (13) and adults with fear of heights (8)
Funding
not stated in the PubMed or Crossref record; authors affiliated with Pharma Foods International Co. Ltd.

Neurotransmitters as food supplements: the effects of GABA on brain and behavior.

Boonstra E, de Kleijn R, Colzato LS. Neurotransmitters as food supplements: the effects of GABA on brain and behavior Front Psychol, 2015. PMID 26500584

Result not recorded
Design
Narrative review
Population
Human and animal studies of oral GABA
Funding
Dutch Research Council (NWO)

Effects of Oral Gamma-Aminobutyric Acid (GABA) Administration on Stress and Sleep in Humans: A Systematic Review.

Hepsomali P, Groeger JA, Nishihira J. Effects of Oral Gamma-Aminobutyric Acid (GABA) Administration on Stress and Sleep in Humans: A Systematic Review Front Neurosci, 2020. PMID 33041752

Result not recorded
Design
Systematic review of 14 placebo-controlled human trials (no meta-analysis)
Population
Healthy adults and poor sleepers in trials of natural or fermentation-produced oral GABA
Funding
Unilever UK Central Resources Limited paid open-access fees; first author employed by Unilever

Search and history

Search (): gaba[ti] AND (stress[tiab]) AND (randomized controlled trial[pt] OR clinical trial[pt]) AND humans[mh]

  • Graded C (proposed): Proposed in the monograph draft
  • C to C (approved): Editor sign-off November 13, 2026: grade matches the editor-approved final page