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GABA and attention: grade C

Limited evidence. Direction: No effect.

Evidence maturity: Early signalShort-term only

Educational guidance, not medical advice

Why this grade

Rubric condition met: Small acute placebo-controlled studies with conflicting results

A 2018 double-blind experiment in young healthy adults found 800 mg improved some measures of temporal attention but not spatial attention. A 2023 double-blind crossover in 32 young adults, using 800 mg, found no effect on temporal attention or working memory and a longer visual search time than placebo. A third small trial (12 per group, 800 mg) found worse task switching, a separate outcome that is not graded here. The results conflict and all are single-dose studies, so the proposal is C with direction none.

How sure are we?

Evidence maturity: Early signal Small acute trials in young healthy adults at 800 mg.

Tested as: GABA (mostly PharmaGABA or rice-germ GABA)

Who paid for the studies
Not stated (treated as not independent)
Risk of bias
Some concerns
Trial registry check
Not checked yet
Outcome measured
A test score, rating scale or performance measure
Who was studied
Matched
Doses used in studies
800 mg single dose
Rules applied
B5: small studies (logged, no further change): All trials under 40
  • Could rise: Would move to C benefit with a preregistered RCT (n of 40 or more) positive on an attention primary.
  • Could fall: Would move to N with two adequately sized null RCTs.

Science is provisional. This grade reflects the evidence we found as of . Next review: .

Maturity sits beside each grade. The grade says what the evidence shows; maturity says how much of it there is and how well it is confirmed.

Established
many trials from several independent teams, including at least one registered in advance
Emerging
two or more trials, or one large registered trial, not yet independently confirmed
Early signal
one trial, small pilots, or results only on secondary outcomes
Mechanistic only
lab, animal or biomarker data, or uncontrolled reports; no controlled human results
Traditional use only
a traditional-use monograph and nothing else

How we grade evidence

Studies this grade rests on

EffectMixedNo effectSize shows participants (n)201520202025RCTCrossover RCTLim 2021, 2021: RCT, n = 48, result not recordedEffects of gamma-aminobutyric acid 2023, 2023: crossover RCT, n = 32, result not recordedLeonte 2018, 2018: RCT, 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
Leonte 20182018RCTnot recordedresult not recorded
Lim 20212021RCT48result not recorded
Effects of gamma-aminobutyric acid 20232023crossover RCT32result not recorded

GABA Supplementation Negatively Affects Cognitive Flexibility Independent of Tyrosine.

Lim LW, Aquili L. GABA Supplementation Negatively Affects Cognitive Flexibility Independent of Tyrosine J Clin Med, 2021. PMID 33919136

Result not recorded
Design
Double-blind, placebo-controlled, randomized four-group experiment (12 per group)
Sample
n = 48
Population
Healthy university students
Funding
No external funding (article fee: Hong Kong Research Grants Council)

Effects of gamma-aminobutyric acid on working memory and attention: A randomized, double-blinded, placebo-controlled, crossover trial.

Tınok AA, Karabay A, Jong J. Effects of gamma-aminobutyric acid on working memory and attention: A randomized, double-blinded, placebo-controlled, crossover trial J Psychopharmacol, 2023. PMID 36988214

Result not recorded
Design
Randomized, double-blind, placebo-controlled crossover trial
Sample
n = 32
Population
Healthy young adults
Funding
No financial support declared

Supplementation of gamma-aminobutyric acid (GABA) affects temporal, but not spatial visual attention.

Leonte A, Colzato LS, Steenbergen L. Supplementation of gamma-aminobutyric acid (GABA) affects temporal, but not spatial visual attention Brain Cogn, 2018. PMID 29222993

Result not recorded
Design
Randomized, double-blind, placebo-controlled single-dose experiment
Population
Young healthy adults
Funding
not stated in the PubMed or Crossref record; full text not read

Search and history

Search (): (gaba[ti] OR aminobutyric[ti]) AND (cognit*[tiab] OR attention[tiab] OR inhibitory control[tiab] OR action selection[tiab]) AND (randomized controlled trial[pt] OR randomised[tiab] OR randomized[tiab])

  • Graded C (awaiting approval)
  • C to C (approved): Editor sign-off November 13, 2026: grade matches the editor-approved final page
  • C to C (approved) (maturity: early signal): Maturity, bias summary and re-check date added