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GABA (gamma-aminobutyric acid)

Status: Phase 2, , not approved for human use
Evidence: Not graded on a research bench yet

GABA (gamma-aminobutyric acid) is an amino acid that serves as the main inhibitory chemical messenger (neurotransmitter) in the brain; the body makes GABA from glutamate, and GABA is also found in foods such as green tea, tomatoes and fermented cheese.

Reviewed 28 October 2026

01Overview

What GABA (gamma-aminobutyric acid) is

Oral GABA is marketed in the United States as a dietary supplement (PMID: 34444905), but whether swallowed GABA crosses the blood-brain barrier is unsettled: animal studies found little entry into the brain, and a 2020 systematic review found no human data on the question (PMID: 6475496; PMID: 11595763; PMID: 33041752). The 14 placebo-controlled human studies of GABA on stress and sleep in that review were small, with 7 to 63 participants each, and 11 had at least one author employed by industry (PMID: 33041752). The review rated the evidence as limited for stress and very limited for sleep (PMID: 33041752).

How it works

GABA in the body

GABA is the main inhibitory neurotransmitter in the human cortex (PMID: 26500584). Cells make GABA from the amino acid glutamate using the enzyme glutamic acid decarboxylase (GAD), which pancreatic beta cells also carry (PMID: 39619323; PMID: 36566274). GABA acts through two receptor families: GABA-A receptors, which are ion channels (ionotropic), and GABA-B receptors, which work through cell signaling cascades (metabotropic); benzodiazepines, barbiturates and several anesthetics act on GABA-A receptors (PMID: 26365137). Outside the brain, GABA is concentrated in pancreatic beta cells (PMID: 39619323), and gut bacteria, including Bacteroides species, actively express GABA-producing pathways in the human gut (PMID: 30531975). GABA is also present in foods such as green tea, tomato and fermented cheese (PMID: 22203366; PMID: 39619323).

Read the full mechanismShow less

Does oral GABA reach the brain?

This is an open question. A 2015 review found that GABA has long been thought unable to cross the blood-brain barrier, but that the studies on the question are often contradictory and use widely varying methods, and the authors called for brain imaging with magnetic resonance spectroscopy after oral GABA (PMID: 26500584). A 2020 systematic review found no data on passage of GABA across the blood-brain barrier in humans; blood GABA rises about 30 minutes after an oral dose, but whether brain GABA rises is unknown (PMID: 33041752; PMID: 30263304). A 2024 review, by contrast, states that oral GABA does not cross the blood-brain barrier (PMID: 39619323).

Rats: radiolabeled GABA injected into the blood entered all brain regions poorly (PMID: 6475496), and GABA left the brain across the barrier at least 16 times faster than it entered, which the authors described as an efflux pump (PMID: 11595763). Intravenous GABA changed the brain's response on functional MRI only after focused ultrasound opened the barrier (PMID: 30659957).
Mice: brain capillary cells carry a GABA transporter (GAT2/BGT-1), which the authors linked to GABA transport across the barrier (PMID: 11598501).
People: EEG studies reported changes in brain wave patterns after oral GABA (PMID: 16971751; PMID: 22203366), which a 2020 review took as limited evidence of an effect on the brain, while noting that human data on barrier passage are missing (PMID: 33041752).

Other routes researchers propose

The 2015 review suggested that any effects of oral GABA might come either from passage into the brain or, more indirectly, through the nerves of the gut (the enteric nervous system) (PMID: 26500584). In mice, GABA given by mouth suppressed short-term food intake, and cutting the sensory fibers of the vagus nerve blunted that effect (PMID: 35745222).

Hormone changes measured in people

Growth hormone: a single 5 g oral dose raised plasma growth hormone in 19 people compared with 18 on placebo, while prolactin rose in only 5 of 15 (PMID: 7376786); in 11 resistance-trained men, 3 g raised resting growth hormone peaks by about 400 percent (PMID: 18091016).
Insulin and glucagon: in 12 healthy volunteers, a single 2 g dose raised fasting insulin 1.6-fold and a week of 2 g three times a day raised it 2.0-fold; fasting glucagon also rose, and blood glucose did not change (PMID: 26617516).

Studied for

Neuroscience
Sleep research
Stress physiology
Endocrinology
Food science
Gut microbiome research

Benefits listed

Shorter time to fall asleep on polysomnography in a 40-person trial (30 on GABA)
Shorter sleep latency and longer non-REM sleep on EEG in a 10-person crossover study
Smaller drop in EEG alpha and beta activity during a stressful mental task (63-person crossover study)
Lower systolic blood pressure with GABA-containing fermented milk or Chlorella in trials of 39 and 80 people

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Higher growth hormone after a single oral dose (studies of 19 and 11 people)
Higher circulating insulin and glucagon in a 12-person pharmacokinetic study

02Research

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What the research shows

No research bench grades GABA (gamma-aminobutyric acid) yet. Benches compare compounds people pair, with the evidence for each.

Key research findings

How much evidence there is

A 2020 systematic review found 14 placebo-controlled human studies of oral GABA, natural or made by fermentation, on stress or sleep, and rated the evidence as limited for stress and very limited for sleep (PMID: 33041752). The studies enrolled 7 to 63 participants each, most tested a single dose, and in 11 of the 14 at least one author was employed by a company; one reviewer selected the studies, and the first author's affiliation was a company research department (PMID: 33041752). A 2015 review likewise noted that most evidence for a calming effect came from researchers with a potential conflict of interest (PMID: 26500584). Several of the human studies had authors from one company in Kyoto, Japan (PMID: 16971751; PMID: 26052150; PMID: 30263304), the same company that filed both GRAS notices for GABA with the FDA (FDA GRAS Notice Inventory, GRN 257 and GRN 595).

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Sleep

Polysomnography trial: in a 4-week double-blind trial of 40 adults with insomnia symptoms (30 on GABA at 300 mg a day from fermented rice germ, 10 on placebo), time to fall asleep on polysomnography fell from 13.4 to 5.7 minutes and sleep efficiency rose from 79.4 to 86.1 percent in the GABA group only (PMID: 29856155). A 2020 review notes that several questionnaire scores in that trial improved within the GABA group without differing from placebo (PMID: 33041752).
EEG crossover studies: in a single-blind crossover study, GABA shortened the time to fall asleep and lengthened non-REM sleep on EEG, and blood GABA peaked 30 minutes after the dose (PMID: 30263304); the 2020 review lists 10 participants (PMID: 33041752). In a second study, 100 mg of GABA shortened sleep latency by 5.3 minutes (PMID: 26052150); the 2020 review lists 16 poor sleepers in that study and classed the result as a trend (PMID: 33041752).
Questionnaire trials: in 30 sedentary women with overweight or obesity who exercised, the group given GABA at 200 mg a day for 90 days showed better sleep efficiency scores, lower depression scores and higher heart rate variability (PMID: 38321713). In a 4-week phase 2 trial in 33 older adults with chronic pain and poor sleep, Pittsburgh Sleep Quality Index scores fell from 11.2 to 8.1 with placebo and from 9.8 to 7.9 with GABA at 500 mg a day; no between-group test is posted (ClinicalTrials.gov NCT04683640 results).
Pattern: the 2020 review found effects on falling asleep but not on staying asleep, and described the sample sizes of the short sleep studies as very low (PMID: 33041752).

Stress

EEG: in 13 adults, GABA raised alpha brain waves and lowered beta waves within an hour compared with water or L-theanine, according to the trial's abstract (PMID: 16971751); a 2020 review lists the dose as 100 mg and classes the beta-wave change as a trend (PMID: 33041752). In a single-blind crossover study of 63 adults aged 20 to 28, 100 mg of GABA lessened the fall in alpha and beta activity during a stressful arithmetic task (PMID: 22203366; PMID: 33041752), though a 2020 review lists self-rated tension, arousal and relaxation as not different from placebo (PMID: 33041752), while the trial's own abstract says its mood questionnaire results matched the brain-wave effect (PMID: 22203366).
Real-life stress: in 8 people with a fear of heights crossing a suspension bridge, saliva immunoglobulin A fell in the placebo group but not in the GABA group (PMID: 16971751).
Overall: the stress studies mostly used single doses of 20 to 100 mg, found mixed effects on heart rate variability, cortisol and chromogranin A, and mostly found no change in self-rated stress (PMID: 33041752).

Blood pressure

In 39 people with mild hypertension, 12 weeks of a fermented milk containing GABA lowered systolic blood pressure by 17.4 mmHg from baseline, more than placebo (P<0.05), in a single-blind trial (PMID: 12627188).
In 80 adults with high-normal blood pressure or borderline hypertension, 12 weeks of GABA-rich Chlorella lowered systolic blood pressure compared with placebo (P<0.01) (PMID: 19811362).
In 30 people with prehypertension or mild to moderate hypertension, bread rich in GABA, potassium and blood-pressure-lowering peptides did not lower 24-hour blood pressure more than other breads (PMID: 26579797).
These products combined GABA with other food components, so the effects cannot be assigned to GABA alone. The USP review found transient, moderate drops of less than 10 percent in some studies (PMID: 34444905).

Hormones and diabetes

Growth hormone rose after single oral doses of 5 g in 19 people (PMID: 7376786) and 3 g in 11 trained men (PMID: 18091016).
In 12 healthy volunteers, GABA raised insulin and glucagon without changing blood glucose (PMID: 26617516).
In a one-year randomized trial in 97 children with new-onset type 1 diabetes, oral GABA alone or combined with GAD-alum, an immunization with the enzyme GAD, did not preserve insulin secretion, the primary outcome; the combination lowered glucagon (PMID: 36566274).

Safety and side effects

In clinical studies

A 2021 safety review by the United States Pharmacopeia (USP) found no serious adverse events linked to GABA in clinical studies at intakes up to 18 g a day for 4 days, or 120 mg a day for 12 weeks, and found no case reports or spontaneous adverse event reports; some studies showed a transient, moderate drop in blood pressure of less than 10 percent (PMID: 34444905). In 12 healthy volunteers, minor adverse events, mainly dizziness and sore throat, were more frequent during a week of 2 g three times a day than during placebo or a single dose, with no serious adverse events (PMID: 26617516). In a 4-week sleep trial of 40 patients, adverse events occurred in 4 (10 percent) (PMID: 29856155). In 80 adults with high-normal blood pressure, 12 weeks of GABA-rich Chlorella produced no adverse events or abnormal laboratory findings (PMID: 19811362). In a one-year trial in 97 children with new-onset type 1 diabetes, the investigators reported that oral GABA was safe and well tolerated (PMID: 36566274).

Read all the safety notesShow less

A registered trial with posted results

In a 4-week phase 2 trial in 33 older adults with chronic pain and poor sleep (18 on GABA at 500 mg a day, 15 on placebo), the posted results list no serious adverse events; the posted non-serious events include balance problems in 9 of 18 on GABA and none of 15 on placebo, and dry throat in 9 of 18 and 3 of 15 (ClinicalTrials.gov NCT04683640 results). The investigators note that the study remained blinded at the time of reporting and that the adverse event table may count repeat events in the same participant (ClinicalTrials.gov NCT04683640 results).

Hormones

Oral GABA changed growth hormone and prolactin responses: 18 g a day for 4 days blunted the growth hormone response and raised the prolactin response to low blood sugar in 8 people (PMID: 7376786), and the USP review advised caution in pregnancy and breastfeeding because of these endocrine effects (PMID: 34444905).

On PubMed

The search "gamma-aminobutyric acid"[MeSH Major Topic] AND "humans"[MeSH Terms] AND ("administration, oral"[MeSH Terms] OR "dietary supplements"[MeSH Terms]) NOT (pregabalin OR gabapentin OR crisugabalin OR mirogabalin OR vigabatrin OR baclofen OR phenibut OR probiotic*) on PubMed.

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03Safety

GABA side effects and interactions

Side effects

Common

Dizziness and sore throat with repeated doses in a 12-person study (PMID: 26617516)
Adverse events in 4 of 40 participants in a 4-week sleep trial (PMID: 29856155)

Serious events

No serious adverse events reported in the clinical studies reviewed by the US Pharmacopeia in 2021 (PMID: 34444905)

Who should not use it

Contraindications

No drug label exists for GABA, so no formal contraindications have been set. Cautions in the literature:

Blood pressure medicines: because some studies found that GABA lowered blood pressure, the USP review judged it conceivable that GABA taken with antihypertensive drugs could raise the risk of low blood pressure (PMID: 34444905).
Pregnancy and breastfeeding: the USP review found no studies in pregnancy or breastfeeding and advised caution because GABA can affect neurotransmitters and hormones such as growth hormone and prolactin (PMID: 34444905).
Drugs that act on the GABA system: registered trials of oral GABA excluded people taking baclofen, benzodiazepines, gabapentin or pregabalin (ClinicalTrials.gov NCT02002130; NCT04683640).
Seizure disorders and low blood pressure: a pediatric diabetes trial excluded children with a history of seizures, and a sleep and pain trial excluded people with low blood pressure (ClinicalTrials.gov NCT02002130; NCT04683640).

Interactions

2 pairings in our record: 1 with a caution and 1 to monitor.

Benzodiazepines, baclofen, gabapentin and pregabalin
Caution

Registered trials of oral GABA excluded people taking baclofen, benzodiazepines, gabapentin or pregabalin (ClinicalTrials.gov NCT02002130; NCT04683640); PubMed lists no interaction study.
Blood pressure medicines
Monitor

Some studies found that GABA lowered blood pressure, and a 2021 USP safety review judged it conceivable that GABA taken with antihypertensive drugs could raise the risk of low blood pressure (PMID: 34444905).

This interaction data is compiled from published research and community reports. It may not be exhaustive. Always consult a healthcare professional before combining compounds.

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04Dosing

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Dosing

No dose on record

Our record lists no dose for GABA (gamma-aminobutyric acid). This section holds what it does list.

Dosing summary

Route: Oral

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Route

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05Prices

GABA (gamma-aminobutyric acid) prices

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06Chemistry

Chemistry and structure

Molecular formula: C4H9NO2
Molecular mass: 103.12 g/mol
CAS number: 56-12-2
Half-life: About 5 hours after oral doses in a 2015 study of 12 healthy volunteers, with peak blood levels 0.5 to 1 hour after dosing (PMID: 26617516); another study found blood GABA highest 30 minutes after an oral dose (PMID: 30263304)

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08Questions

Frequently asked questions

What is GABA?

GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the brain, and the body makes GABA from glutamate (PMID: 26500584; PMID: 39619323). GABA is also found in foods such as green tea, tomato and fermented cheese (PMID: 22203366; PMID: 39619323). GABA is marketed in the United States as a dietary supplement (PMID: 34444905).

Does oral GABA cross the blood-brain barrier?

Whether oral GABA crosses the blood-brain barrier is unsettled, and a 2015 review found the studies of GABA and the barrier contradictory and varied in method (PMID: 26500584). In rats, injected GABA entered the brain poorly and left the brain at least 16 times faster than it entered (PMID: 6475496; PMID: 11595763). A 2020 systematic review found no human data on GABA crossing the blood-brain barrier (PMID: 33041752). A 2024 review states that oral GABA does not cross the barrier (PMID: 39619323).

Does GABA improve sleep?

A 2020 systematic review rated the evidence for oral GABA and sleep as very limited (PMID: 33041752). In a 40-person polysomnography trial of GABA, time to fall asleep fell from 13.4 to 5.7 minutes in the 30-person GABA group (PMID: 29856155). In a 33-person phase 2 trial, Pittsburgh sleep quality scores improved by 1.9 points with GABA and by 3.1 points with placebo, and no comparison between the groups is posted (ClinicalTrials.gov NCT04683640 results).

Does GABA reduce stress?

A 2020 systematic review rated the evidence for oral GABA and stress as limited, based on studies of 7 to 63 people that mostly tested single doses (PMID: 33041752). In a 63-person crossover study, GABA lessened changes in brain waves during a stressful task (PMID: 22203366), but a 2020 review reports that self-rated tension and relaxation with GABA did not differ from placebo (PMID: 33041752). Most evidence for a calming effect of GABA came from researchers with a potential conflict of interest (PMID: 26500584).

Is GABA approved by the FDA?

GABA is not an FDA-approved drug, and Drugs@FDA lists no product with GABA as its active ingredient (openFDA search, 25 October 2026). GABA is marketed in the United States as a dietary supplement (PMID: 34444905), a category the FDA does not approve before marketing (FDA, Questions and Answers on Dietary Supplements). Two GRAS notices for GABA as a food ingredient, filed with the FDA in 2008 and 2015, were closed when the notifier asked the FDA to stop evaluating them (FDA GRAS Notice Inventory, GRN 257 and GRN 595).

Does GABA lower blood pressure?

GABA-containing fermented milk lowered systolic blood pressure more than placebo in a 39-person trial (PMID: 12627188), and GABA-rich Chlorella lowered systolic blood pressure in an 80-person trial (PMID: 19811362). GABA-enriched bread did not lower 24-hour blood pressure more than other breads in a 30-person trial (PMID: 26579797). The USP safety review found transient blood pressure drops of less than 10 percent with GABA in some studies (PMID: 34444905).

What side effects have GABA studies reported?

A 2021 US Pharmacopeia review found no serious adverse events with GABA in clinical studies at up to 18 g a day for 4 days (PMID: 34444905). Repeated 2 g doses of GABA three times a day brought minor dizziness and sore throat in a 12-person study (PMID: 26617516). Oral GABA also raised growth hormone after single large doses (PMID: 7376786; PMID: 18091016), and the USP review advised caution with GABA in pregnancy and breastfeeding because GABA can affect hormones such as growth hormone and prolactin (PMID: 34444905).

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