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GABA and blood pressure: grade C

Limited evidence. Direction: Benefit.

C LimitedShort-term only

Educational guidance, not medical advice

Why this grade

Rubric condition met: Two small RCTs in people with high-normal to mildly raised blood pressure, using GABA in a fermented milk or a Chlorella supplement

In a single-blind trial of 39 adults with mild hypertension, a GABA-containing fermented milk for 12 weeks lowered systolic blood pressure more than placebo. In a double-blind trial of 80 adults with high-normal blood pressure or borderline hypertension, GABA-rich Chlorella (20 mg GABA twice daily) for 12 weeks lowered systolic blood pressure compared with placebo. In 52 adults with prediabetes taking 500 mg of GABA three times a day for 95 days, blood pressure was a secondary outcome and showed no significant effect after correction for multiple testing. The positive trials tested GABA within a fermented milk or a Chlorella supplement in people with raised blood pressure, so the proposal is C, with that context on the grade.

How we grade evidence

Studies this grade rests on

EffectMixedNo effectSize shows participants (n)200020052010201520202025RCTSafety review (us…Shimada 2009, 2009: RCT, n = 80, result not recordedEffects of γ-aminobutyric acid 2023, 2023: RCT, n = 52, result not recordedInoue 2003, 2003: RCT, n = 39, result not recordedOketch-Rabah 2021, 2021: safety review (usp dietary supplement admission evaluation), 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
Inoue 20032003RCT39result not recorded
Shimada 20092009RCT80result not recorded
Oketch-Rabah 20212021safety review (usp dietary supplement admission evaluation)not recordedresult not recorded
Effects of γ-aminobutyric acid 20232023RCT52result not recorded

Anti-hypertensive effect of gamma-aminobutyric acid (GABA)-rich Chlorella on high-normal blood pressure and borderline hypertension in placebo-controlled double blind study.

Shimada M, Hasegawa T, Nishimura C. Anti-hypertensive effect of gamma-aminobutyric acid (GABA)-rich Chlorella on high-normal blood pressure and borderline hypertension in placebo-controlled double blind study Clin Exp Hypertens, 2009. PMID 19811362

Result not recorded
Design
Randomized, placebo-controlled, double-blind trial
Sample
n = 80
Population
Adults with high-normal blood pressure or borderline hypertension
Funding
not stated in the PubMed or Crossref record; full text not read

Blood-pressure-lowering effect of a novel fermented milk containing gamma-aminobutyric acid (GABA) in mild hypertensives.

Inoue K, Shirai T, Ochiai H. Blood-pressure-lowering effect of a novel fermented milk containing gamma-aminobutyric acid (GABA) in mild hypertensives Eur J Clin Nutr, 2003. PMID 12627188

Result not recorded
Design
Randomized, placebo-controlled, single-blind trial
Sample
n = 39
Population
Adults with mild hypertension (clinical population)
Funding
not stated in the PubMed or Crossref record; full text not read

Effects of γ-aminobutyric acid supplementation on glucose control in adults with prediabetes: A double-blind, randomized, placebo-controlled trial.

de Bie TH, Witkamp RF, Balvers MG. Effects of γ-aminobutyric acid supplementation on glucose control in adults with prediabetes: A double-blind, randomized, placebo-controlled trial Am J Clin Nutr, 2023. PMID 37495019

Result not recorded
Design
Randomized, double-blind, placebo-controlled, parallel-arm trial
Sample
n = 52
Population
Adults aged 50 to 70 with prediabetes (clinical population)
Funding
Topsector Agri & Food; Dutch Ministry of Economic Affairs (Crossref funder list)

United States Pharmacopeia (USP) Safety Review of Gamma-Aminobutyric Acid (GABA).

Oketch-Rabah HA, Madden EF, Roe AL. United States Pharmacopeia (USP) Safety Review of Gamma-Aminobutyric Acid (GABA) Nutrients, 2021. PMID 34444905

Result not recorded
Design
Safety review (USP dietary supplement admission evaluation)
Population
Human clinical studies, adverse event reports and animal toxicology
Funding
No external funding (USP review; one author affiliated with The Procter & Gamble Company)

Search and history

Search (): gaba[ti] AND (blood pressure[tiab]) AND (randomized controlled trial[pt] OR meta-analysis[pt])

  • 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