Vitamins & Supplements · Nootropic
GABA Supplements
Gamma-aminobutyric acid; 4-aminobutanoic acid · also called GABA, oral GABA, gamma-aminobutyric acid
GABA is the main calming chemical messenger in the brain, and it is sold in capsules and foods for stress and sleep. Nobody has shown that GABA taken by mouth reaches the brain. Reviews find limited evidence for stress and very limited evidence for sleep. Phenibut, a GABA look-alike drug, is not GABA and can cause serious harm.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About GABA Supplements
GABA is the brain's main calming messenger, and the body makes it. Capsules and foods with GABA are sold for stress and sleep, but it is not known whether GABA taken by mouth reaches the brain. Reviews find limited evidence for stress and very limited evidence for sleep. Phenibut, a look-alike drug, has caused serious poisonings and withdrawal.
What GABA is
GABA (gamma-aminobutyric acid) is a non-proteinogenic amino acid, which means the body does not use it to build proteins. It is the main inhibitory (calming) chemical messenger in the mammalian brain.
This is the body's own GABA doing its normal job. It is not proof that GABA from a pill does anything. GABA is not an essential nutrient, and no deficiency state is described in the sources we read.
Where it comes from
A 2023 trial abstract says GABA from foods such as tomatoes and fermented foods can be considerable. No source we read gave GABA amounts per food portion, so this page gives none.
GABA is also sold as capsules, tablets and powders, and in calm and sleep blends. Several trials used GABA made by fermentation, for example in fermented milk. That is not the same as a capsule.
What the research shows
A 2020 systematic review of 14 placebo-controlled trials found limited evidence for stress benefits and very limited evidence for sleep benefits. It included only GABA from foods or fermentation, and one of its authors works at a consumer-goods company.
A 2015 review says it is unclear whether GABA supplements do more than a placebo, and most of the evidence for a calming effect came from researchers with a possible conflict of interest.
A 95-day trial of GABA capsules in 52 adults with prediabetes found no change in blood glucose or in any other measure at group level. A small 2003 trial found lower systolic blood pressure with a GABA fermented milk. We found no trial in people with a diagnosed anxiety disorder.
Capsules versus fermented foods
The trials behind the stress and sleep review used GABA from foods or fermentation. The blood pressure trial used a fermented milk, and the glucose trial used pure GABA capsules.
Results from one kind of product cannot be assumed for another, and no study compared them.
At a glance
Traditional uses history, not proof
- Not a traditional remedy: the body makes GABA itself
- Found in some foods, such as tomatoes and fermented foods
- Sold as capsules, tablets, powders and in calm and sleep blends
Studied for research
- Stress (oral GABA from foods or fermentation), low certainty
- Sleep, very low certainty
- Whether oral GABA reaches the brain, insufficient evidence
- Anxiety disorders, insufficient evidence (no studies found)
- Blood pressure (mostly fermented milk), very low certainty
- Blood glucose in prediabetes (capsules), low certainty: no effect found
Main compounds
- Gamma-aminobutyric acid (GABA)
- Phenibut (a GABA-like drug, covered only as a warning)
Common forms
- Capsules, tablets and powders
- GABA-enriched and fermented foods, such as fermented milk
- Calm and sleep blends
Research links: 2020 systematic review: oral GABA and stress and sleep (14 trials) · 2015 review: GABA food supplements and the blood-brain barrier · 2021 USP safety review of GABA · 2023 trial: GABA capsules in adults with prediabetes (52 people) · 2023 systematic review: phenibut toxicity and withdrawal (62 cases) · 2019 FDA update on phenibut in dietary supplements · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Gamma-aminobutyric acid (GABA; 4-aminobutanoic acid)
- Synonyms
- GABA; gamma-aminobutyric acid; gamma-amino butyric acid; 4-aminobutanoic acid; oral GABA
- Common names
- GABA (English); Oral GABA (English)
- Family or group
- A non-proteinogenic amino acid (not used to build proteins) that is the main inhibitory (calming) chemical messenger in the mammalian brain.
- Look-alikes and adulterants
- Name: Phenibut; Note: A GABA-like drug (4-amino-3-phenylbutanoic acid, PubChem CID 14113) made in Russia in the early 1960s. It acts mainly on the GABA type B receptor and is a different substance, not a form of GABA.; Name: GABA-enriched foods and fermented products; Note: Foods or ferments that contain GABA, used in many of the stress and sleep trials; different from a capsule.
- Sustainability and conservation
- Not assessed.
Traditional use and history history, not clinical proof
| Tradition or era | Documented use | Source |
|---|---|---|
| PubMed 38339875 abstract, read 2026-10-26. |
Traditional use shows how it was used. It does not show that it works or is safe today.
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| Gamma-aminobutyric acid (GABA) PubChem 119 | amino acid neurotransmitter | Not read from a source. | Studied for stress, sleep, blood pressure and blood glucose; see the Benefits tab. 4 | Human data |
| Phenibut PubChem 14113 | GABA analog (a different drug) | Found at 21 mg to 1,164 mg per serving in four tested supplement brands after the FDA warnings. | Acts mainly on the GABA type B receptor; causes dependence, toxicity and withdrawal. 3 2 | Human case reports |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Main calming messenger in the brain | GABA receptors (not named further in the abstracts read) | GABA is the main inhibitory neurotransmitter in the mammalian brain. This describes the body's own GABA, not the effect of a supplement. 4 1 | Established physiology |
| Crossing the blood-brain barrier | Not specified | Studies on whether oral GABA crosses are often contradictory. Any effect might come through the barrier or indirectly via the enteric (gut) nervous system. 1 | Proposed, unresolved |
| Blood pressure | Not specified | A short, moderate drop in blood pressure was seen in some studies; how is not described in the abstracts read. 6 | Human, mechanism not described |
| Growth hormone and prolactin | Not specified | The USP review says GABA can increase growth hormone and prolactin levels. 6 | Human and review, details not in the abstract |
Absorption, metabolism and elimination
- Absorption
- Not described in the abstracts read.
- Distribution
- Whether oral GABA reaches the brain is unresolved (see the Benefits tab).
- Metabolism
- Not described in the abstracts read.
- Elimination
- Not described in the abstracts read.
- Bioavailability
- Not compared between capsules, fermented foods and food sources in the sources read.
Isolated compounds versus whole extracts
Trials in the stress and sleep review used GABA that is naturally in foods or made by fermentation, and the blood pressure trial used a fermented milk. The glucose trial used pure GABA capsules. Results from one kind of product cannot be assumed for another.
Nutritional composition
A 2023 trial abstract says GABA from tomatoes and fermented foods can be considerable, but no source read gave GABA amounts per food portion (no USDA or NIH Office of Dietary Supplements table was read), so none are given here. GABA is not an essential nutrient and no deficiency state is described.
2 low certainty2 very low certainty2 not enough evidence
What was looked at
The 6 benefits and uses checked for GABA Supplements, each with how strong the evidence is. Tap one to open it.
- Stress (oral GABA from foods or fermentation)Low certainty
- Sleep (oral GABA from foods or fermentation)Very low certainty
- Does GABA taken by mouth reach the brain?Not enough evidence
- Anxiety disordersNot enough evidence
- Blood pressure (mostly GABA in fermented milk)Very low certainty
- Blood glucose in prediabetes (GABA capsules)Low certainty
Lab markers tracked in the studies
Self-reported sleep qualitySystolic blood pressureBlood glucose after a sugar drink test
What is GABA Supplements good for?
The main studied uses and how strong the human evidence is for each. The body's own GABA does calm the brain, but that does not show a GABA pill works.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
Stress (oral GABA from foods or fermentation)
Low certaintyA systematic review of 14 placebo-controlled trials found limited evidence that oral GABA eases stress. The trials mostly used GABA from foods or fermentation, not standard capsules.
2 studiesGABA naturally present in foods or made by fermentation, by mouth. Am…
Studies, doses and limits
What the trials found
A 2020 systematic review of 14 placebo-controlled human trials of natural or fermentation-made oral GABA looked at stress and related body measures. A 2015 review noted that most of the evidence for a calming effect came from researchers with a possible conflict of interest.
Results
Limited evidence for stress benefits. The authors say more studies are needed before any conclusion about whether oral GABA works.
Effect sizes as reported
No pooled numbers in the abstract.
Why this rating
Mixed results in small trials, GABA given in foods rather than capsules, and a possible conflict of interest in much of the supportive work.
Form and dose studied
GABA naturally present in foods or made by fermentation, by mouth. Amounts are not given in the abstract.
Who was studied
Human participants; details are not in the abstract.
Limits
Only PubMed was searched. Trial amounts, products and stress measures differed. One review author works at Unilever R&D.
Why researchers looked
GABA is the main calming chemical messenger in the brain, so makers sell it for calm and stress.
Traditional use
Not a traditional remedy and not an essential nutrient. GABA is made by the body and also occurs in some foods, such as tomatoes and fermented foods.
Proposed mechanism Proposed, unresolved
Not established in people. The 2015 review says how oral GABA might act is unknown: it may cross the blood-brain barrier, or act more indirectly through the gut nervous system. Studies on crossing the barrier are contradictory.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab: no serious adverse events at the intakes studied, a small short drop in blood pressure, and no data in pregnancy.
Sleep (oral GABA from foods or fermentation)
Very low certaintyThe same review found very limited evidence that oral GABA helps sleep. One trial of GABA capsules in adults with prediabetes found no change in self-reported sleep quality.
2 studiesReview: GABA from foods or fermentation. Prediabetes trial: pure GABA…
Studies, doses and limits
What the trials found
The 2020 systematic review of 14 trials looked at sleep as well as stress. In a separate 95-day trial in 52 adults with prediabetes, self-reported sleep quality was a secondary measure.
Results
Very limited evidence for sleep benefits in the review. In the prediabetes trial no secondary measure, including sleep quality, changed at group level after correcting for chance findings.
Effect sizes as reported
No pooled numbers in the review abstract. The prediabetes trial abstract gives no sleep numbers.
Why this rating
Very limited trial evidence; the one capsule trial was not designed to test sleep.
Form and dose studied
Review: GABA from foods or fermentation. Prediabetes trial: pure GABA capsules, 500 mg three times daily for 95 days (as studied, not advice).
Who was studied
Human participants in the review (details not in the abstract); adults aged 50 to 70 with prediabetes in the capsule trial.
Limits
Sleep was a minor question in a small set of trials. The prediabetes result is a secondary outcome in people who did not have a sleep problem.
Why researchers looked
GABA calms nerve activity, so it is sold in sleep products.
Traditional use
Not a traditional remedy and not an essential nutrient. GABA is made by the body and also occurs in some foods, such as tomatoes and fermented foods.
Proposed mechanism Proposed, unresolved
Not established in people. The 2015 review says how oral GABA might act is unknown: it may cross the blood-brain barrier, or act more indirectly through the gut nervous system. Studies on crossing the barrier are contradictory.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab.
Does GABA taken by mouth reach the brain?
Not enough evidenceNobody knows yet. Studies on whether GABA crosses the protective barrier around the brain are contradictory, and no one has measured brain GABA after an oral dose in the work we read.
1 studiesNot applicable.
Studies, doses and limits
What the trials found
A 2015 review says it has long been thought that GABA cannot cross the blood-brain barrier, but the studies are often contradictory and use very different methods. It calls for brain-scan measurements of GABA in people after oral doses.
Results
Unresolved. Any effect might come through the barrier or more indirectly through the nervous system of the gut. The authors conclude the mechanism of GABA food supplements is far from clear.
Why this rating
Contradictory studies and no direct human brain measurement in the review.
Limits
A 2015 narrative review; newer work may exist. We did not find a human brain-scan study of oral GABA in our search.
Why researchers looked
If a pill cannot reach the brain, a calming effect there would be hard to explain.
Traditional use
Not a traditional remedy and not an essential nutrient. GABA is made by the body and also occurs in some foods, such as tomatoes and fermented foods.
Proposed mechanism Proposed, unresolved
Not established in people. The 2015 review says how oral GABA might act is unknown: it may cross the blood-brain barrier, or act more indirectly through the gut nervous system. Studies on crossing the barrier are contradictory.
A proposed mechanism does not show that the effect happens in people.
Not applicable.
Anxiety disorders
Not enough evidenceWe found no trial or review of oral GABA in people diagnosed with an anxiety disorder, so there is no evidence either way.
1 studiesNot applicable.
Studies, doses and limits
What the trials found
PubMed searches in October 2026 for oral GABA and anxiety trials found no study of oral GABA in a diagnosed anxiety disorder.
Results
No evidence found. A phenibut look-alike drug has been used for anxiety in Russia, but phenibut is a different drug (see the Safety tab).
Why this rating
No studies found.
Limits
Based on our own searches, which may have missed work.
Why researchers looked
GABA is linked to calming activity in the brain, so it is marketed for anxiety.
Traditional use
Not a traditional remedy and not an essential nutrient. GABA is made by the body and also occurs in some foods, such as tomatoes and fermented foods.
Proposed mechanism Proposed, unresolved
Not established in people. The 2015 review says how oral GABA might act is unknown: it may cross the blood-brain barrier, or act more indirectly through the gut nervous system. Studies on crossing the barrier are contradictory.
A proposed mechanism does not show that the effect happens in people.
Anxiety that lasts deserves a proper assessment by a clinician.
Blood pressure (mostly GABA in fermented milk)
Very low certaintyA small 2003 trial of GABA-containing fermented milk in people with mild high blood pressure found lower systolic pressure than placebo. A USP safety review says GABA studies show a small, short drop in blood pressure.
3 studiesA fermented milk with GABA (trial 2003); pure GABA capsules in the pr…
Studies, doses and limits
What the trials found
A 2003 randomised single-blind trial gave 39 adults with mild high blood pressure fermented milk with GABA or placebo for 12 weeks. The 2021 USP safety review pooled what the studies showed on safety and noted a transient, moderate drop in blood pressure.
Results
Systolic pressure at 12 weeks was 17.4 mmHg below the start in the fermented-milk group and differed from placebo (P below 0.05). The USP review reports a drop of under 10% that did not last. In the 95-day capsule trial in prediabetes, blood pressure did not change at group level.
Effect sizes as reported
Fermented-milk trial: systolic -17.4 mmHg and diastolic -7.2 mmHg from baseline. USP: change under 10%, transient.
Why this rating
One small, single-blind, 2003 trial with a food product (not GABA alone), a short-lived effect in the safety review, and a null result for capsules in a later trial.
Form and dose studied
A fermented milk with GABA (trial 2003); pure GABA capsules in the prediabetes trial. Trial amounts are in the studies table only.
Who was studied
Adults with mild high blood pressure (fermented milk trial); adults with prediabetes (capsule trial).
Limits
Single-blind, small, one trial. The effect of a fermented milk cannot be assumed for capsules. Funding not stated in the abstract.
Why researchers looked
Some studies noted that blood pressure fell after GABA, so it has been tested in people with mild high blood pressure.
Traditional use
Not a traditional remedy and not an essential nutrient. GABA is made by the body and also occurs in some foods, such as tomatoes and fermented foods.
Proposed mechanism Not described
Not established. The abstracts read do not describe how GABA might lower blood pressure.
A proposed mechanism does not show that the effect happens in people.
A drop in blood pressure matters for anyone on blood pressure medicine. See the Safety tab.
Blood glucose in prediabetes (GABA capsules)
Low certaintyA 95-day trial in 52 adults with prediabetes found GABA capsules did not change blood glucose after a sugar drink test.
1 studiesPure GABA capsules, 500 mg three times daily for 95 days (as studied,…
Studies, doses and limits
What the trials found
A 2023 double-blind randomised placebo-controlled trial (NCT04303468) in 52 adults aged 50 to 70 with prediabetes and a body mass index of 25 or more.
Results
Compared with placebo, GABA did not change the blood glucose response after the sugar drink test. After correcting for chance findings, no secondary measure changed at group level: HbA1c, insulin, glucagon, glucose swings, blood fats, blood pressure or the GABA level in blood.
Effect sizes as reported
Difference in glucose response 0.21 mmol/L (95% CI -0.252 to 0.674; P = 0.364).
Why this rating
One well-designed but small trial in one group of people, with a clear null result on its main question.
Form and dose studied
Pure GABA capsules, 500 mg three times daily for 95 days (as studied, not advice).
Who was studied
Adults aged 50 to 70 with prediabetes.
Limits
Small, one trial, one population. The authors suggest studying people with advanced diabetes or other heart-and-metabolism problems. Funding not stated in the abstract.
Why researchers looked
Rodent studies had suggested oral GABA might help glucose control and heart health, but this had not been tested in people.
Traditional use
Not a traditional remedy and not an essential nutrient. GABA is made by the body and also occurs in some foods, such as tomatoes and fermented foods.
Proposed mechanism Animal research
The trial abstract says rodent studies showed benefits on glucose control and heart health. That is animal data only.
A proposed mechanism does not show that the effect happens in people.
The abstract does not report side effects.
Connections to the rest of health
How GABA Supplements connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Stress Reduction | Low certainty | Stress (oral GABA from foods or fermentation): A systematic review of 14 placebo-controlled trials found limited evidence that oral GABA eases stress. The trials mostly used GABA from foods or fermentation, not standard capsules. | 4 1 | |
| Calm Relaxation | Low certainty | Stress (oral GABA from foods or fermentation): A systematic review of 14 placebo-controlled trials found limited evidence that oral GABA eases stress. The trials mostly used GABA from foods or fermentation, not standard capsules. | 4 1 | |
| Better Sleep | Very low certainty | Sleep (oral GABA from foods or fermentation): The same review found very limited evidence that oral GABA helps sleep. One trial of GABA capsules in adults with prediabetes found no change in self-reported sleep quality. | 4 10 | |
| Calm Relaxation | Not enough evidence | Does GABA taken by mouth reach the brain?: Nobody knows yet. Studies on whether GABA crosses the protective barrier around the brain are contradictory, and no one has measured brain GABA after an oral dose in the work we read. | 1 | |
| Anxiety Support | Not enough evidence | Anxiety disorders: We found no trial or review of oral GABA in people diagnosed with an anxiety disorder, so there is no evidence either way. | 1 | |
| Blood Pressure Support | Very low certainty | Blood pressure (mostly GABA in fermented milk): A small 2003 trial of GABA-containing fermented milk in people with mild high blood pressure found lower systolic pressure than placebo. A USP safety review says GABA studies show a small, short drop in blood pressure. | 5 6 10 | |
| Blood Sugar Balance | Low certainty | Blood glucose in prediabetes (GABA capsules): A 95-day trial in 52 adults with prediabetes found GABA capsules did not change blood glucose after a sugar drink test. | 10 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Stress Mood | Biological association | Low certainty | Studied for: Stress (oral GABA from foods or fermentation) Studied for: Anxiety disorders | 4 1 |
| Brain Focus | Biological association | Low certainty | Studied for: Stress (oral GABA from foods or fermentation) Studied for: Does GABA taken by mouth reach the brain? | 4 1 |
| Sleep Recovery | Biological association | Very low certainty | Studied for: Sleep (oral GABA from foods or fermentation) | 4 10 |
| Cardiovascular System | Biological association | Very low certainty | Studied for: Blood pressure (mostly GABA in fermented milk) | 5 6 10 |
| Blood Sugar Support | Biological association | Low certainty | Studied for: Blood glucose in prediabetes (GABA capsules) | 10 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Self-reported sleep quality | Biological association | Very low certainty | Measured in trials: no clear change with GABA. A lab change is not the same as a health benefit. | 10 |
| Systolic blood pressure | Biological association | Very low certainty | Measured in trials: lower with GABA fermented milk than placebo in one trial; no change with capsules in another. A lab change is not the same as a health benefit. | 5 10 |
| Blood glucose after a sugar drink test | Biological association | Low certainty | Measured in trials: no difference from placebo. A lab change is not the same as a health benefit. | 10 |
K. Biological pathways
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Phenibut | Preliminary mechanism | Review | A GABA analog often confused with GABA; it acts on the GABA type B receptor. | 3 |
| L-theanine | Preliminary mechanism | No study read here | A different calming ingredient; covered on its own page. |
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Gamma-aminobutyric acid (GABA) | Biological association | Human | Studied for stress, sleep, blood pressure and blood glucose; see the Benefits tab. | 4 |
| Phenibut | Biological association | Human case reports | Acts mainly on the GABA type B receptor; causes dependence, toxicity and withdrawal. | 3 2 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
Evidence at a glance: what the research found for 6 outcomes
Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.
The evidence
The research centre for GABA Supplements. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing summary and re-read the PubMed abstracts for the reviews and trials, plus the FDA page on phenibut. Only abstracts were read for studies. The NIH Office of Dietary Supplements was not checked and is marked unverified.
Study library: every study we checked 10
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Boonstra 2015 Neurotransmitters as food supplements: the effects of GABA on brain and behavior. Front Psychol · PMID 26500584 · DOI |
Narrative review |
Review of what is known about GABA food supplements, the blood-brain barrier and behaviour. | GABA food supplements Oral |
The authors say it is unclear whether the supplements do more than a placebo, and that how they might work is unknown. Studies of whether GABA crosses the blood-brain barrier are often contradictory. There is some evidence for a calming effect, but most came from researchers with a possible conflict of interest. Not applicable (Not applicable) Methods, limits and fundingOutcomes: Whether oral GABA reaches the brain; effects on behaviour Limitations: A narrative review (not a systematic search). Published in 2015, so newer work is not covered. Funding and conflicts: Authors from Leiden and Amsterdam universities and the Max Planck Institute; funding not stated in the abstract. Read: abstract |
| Cohen 2022 Quantity of phenibut in dietary supplements before and after FDA warnings. Clin Toxicol (Phila) · PMID 34550038 · DOI |
Laboratory product analysis product testing |
4 Four brands of over-the-counter supplements that listed phenibut, tested before and after the FDA warnings. |
Phenibut supplements (not GABA) Oral Found 484 mg and 487 mg per serving in two brands before the warnings; 21 mg to 1,164 mg after |
Before the FDA warnings two of four brands contained phenibut. After them all four did, and the amount rose in three of four. Amounts per serving were up to 450% more than a typical 250 mg Russian pharmaceutical tablet. Amount rose in 3 of 4 brands (Not applicable) Methods, limits and fundingOutcomes: Whether phenibut was present and how much per serving Limitations: Only four brands were tested. It shows what was in these products at the time, not in all products. Funding and conflicts: Funding not stated in the abstract. Authors include researchers at NSF International and a university laboratory. Read: abstract |
| Feldman 2023 A systematic review of phenibut withdrawal focusing on complications, therapeutic approaches, and single substance versus polysubstance withdrawal. Clin Toxicol (Phila) · PMID 38112312 · DOI |
Systematic review |
25 25 case reports or conference abstracts of phenibut withdrawal (all male, median age 30). |
Phenibut (a GABA-like drug, not GABA) Oral Median daily use before withdrawal 10 g (reported range 1 to 200 g) Shortest use before withdrawal was one week |
Withdrawal could start within two hours of the last dose. Seizures occurred in 8%, intubation in 24% and intensive care admission in 44%. Withdrawal was similar in people using phenibut alone and those using other drugs too. All people who stopped suddenly were admitted to hospital. 44% intensive care admission (Not applicable) Methods, limits and fundingOutcomes: Withdrawal symptoms, complications and treatment Limitations: Case reports only, with possible publication bias. The amount in the product may not have matched what the person believed they took. Funding and conflicts: Funding not stated in the abstract. Read: abstract |
| Hepsomali 2020 Effects of Oral Gamma-Aminobutyric Acid (GABA) Administration on Stress and Sleep in Humans: A Systematic Review. Front Neurosci · PMID 33041752 · DOI |
Systematic review |
Fourteen placebo-controlled human trials of GABA eaten in foods or made by fermentation, searched up to February 2020. | GABA (natural, from foods, or made by fermentation) Oral, in foods or fermented products Varied between trials; not reported in the abstract Not reported in the abstract · vs Placebo |
The authors found limited evidence for stress benefits and very limited evidence for sleep benefits. They say more studies are needed before any conclusion about whether oral GABA works. No pooled numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Stress, sleep and related body measures Limitations: Only GABA from foods or fermentation was included, not standard capsules. Only PubMed was searched. Results across the trials were mixed. Funding and conflicts: Funding not stated in the abstract. One author works at Unilever R&D (affiliation shown in the abstract). Read: abstract |
| Inoue 2003 Blood-pressure-lowering effect of a novel fermented milk containing gamma-aminobutyric acid (GABA) in mild hypertensives. Eur J Clin Nutr · PMID 12627188 · DOI |
Randomised controlled trial |
39 39 adults aged 28 to 81 with mild high blood pressure, in Tokyo. |
Fermented milk containing GABA (a food, not a capsule) Oral, daily fermented milk 12 weeks, then 2 weeks without · vs Placebo (single-blind) |
Blood pressure fell within 2 to 4 weeks and stayed lower over the 12 weeks. After 12 weeks, systolic pressure was 17.4 mmHg lower and diastolic 7.2 mmHg lower than at the start in the fermented-milk group. Only the systolic pressure differed from placebo. Heart rate, weight and routine blood and urine tests did not change. Systolic -17.4 mmHg, diastolic -7.2 mmHg from baseline (SD 4.3 and 5.7) (Not given in the abstract) Methods, limits and fundingOutcomes: Seated blood pressure and heart rate; routine blood and urine tests Limitations: Single-blind (the researchers knew who got which product), small, 2003. The product was a milk with other fermentation products, so GABA alone cannot be credited. Funding and conflicts: Funding not stated in the abstract. Read: abstract |
| Oketch-Rabah 2021 United States Pharmacopeia (USP) Safety Review of Gamma-Aminobutyric Acid (GABA). Nutrients · PMID 34444905 · DOI |
Safety review |
USP review of clinical studies, adverse-event information and toxicology data on GABA as a supplement or as a natural part of fermented milk or soy. | GABA (pure, or in fermented milk or soy) Oral Up to 18 g a day for 4 days; 120 mg a day for 12 weeks in longer studies (as reported in the abstract) 4 days to 12 weeks |
No serious adverse events at the intakes studied. Some studies showed a short, moderate drop in blood pressure (under 10%). No studies in pregnancy or breastfeeding, and no case reports of adverse events were found. Rats and dogs given up to 1 g per kg a day for a long time showed no signs of toxicity. The authors say caution is advised in pregnancy and breastfeeding. Blood pressure change under 10% (transient) (Not given in the abstract) Methods, limits and fundingOutcomes: Serious adverse events, blood pressure, effects in pregnancy and breastfeeding, animal toxicity Limitations: The studies were short and mostly small. No evidence exists for pregnancy or breastfeeding, and the review does not cover long-term use in people. Funding and conflicts: Authors work at the U.S. Pharmacopeial Convention, The Procter & Gamble Company and the NIH Office of Dietary Supplements. The authors declare no conflict of interest. Read: abstract |
| Penzak 2024 Phenibut: Review and Pharmacologic Approaches to Treating Withdrawal. J Clin Pharmacol · PMID 38339875 · DOI |
Narrative review |
29 Review of phenibut pharmacology, intoxication, regulation and treatment of withdrawal (29 withdrawal cases). |
Phenibut (a GABA-like drug, not GABA) Oral |
Phenibut is a GABA look-alike first made in Russia in the early 1960s, sold online as a nootropic. The authors say there are no comparative studies of withdrawal treatment and that cases are likely to increase while it stays legal in the USA. Urine or blood tests for phenibut are not widely available, so doctors need a detailed history of what the person took. Not applicable (Not applicable) Methods, limits and fundingOutcomes: Pharmacology, intoxication and withdrawal treatment Limitations: A review of case reports; no comparative studies exist. Funding and conflicts: Funding not stated in the abstract. Read: abstract |
| U.S. Food and Drug Administration 2019 FDA Acts on Dietary Supplements Containing DMHA and Phenibut (HFP Constituent Update) FDA Human Foods Program constituent update, April 16, 2019 · Source |
Regulator notice not applicable |
Three warning letters about products labelled as dietary supplements that list phenibut. | Phenibut (a GABA-like drug, not GABA) |
The FDA says phenibut has been found in products labelled as dietary supplements, sometimes marketed as a sleep aid. It says phenibut does not meet the definition of a dietary ingredient, and products that list it as a dietary ingredient are misbranded. Not applicable (Not applicable) Methods, limits and fundingOutcomes: Legal status of phenibut in supplements Limitations: A 2019 notice about phenibut only. It is not a ruling on GABA. Funding and conflicts: Government agency. Read: page text, 2026-10-26 |
| Weleff 2023 Clinical Presentations and Treatment of Phenibut Toxicity and Withdrawal: A Systematic Literature Review. J Addict Med · PMID 37579098 · DOI |
Systematic review |
62 62 published cases from 36 studies of phenibut toxicity or withdrawal (80.7% male, average age 30.9 years). |
Phenibut (a GABA-like drug, not GABA) Oral |
86.8% got phenibut online and 63.2% also used other addictive substances, mostly benzodiazepines and alcohol. Toxicity caused altered mental status, sleepiness, psychosis and movement problems, and 48.7% of toxicity cases needed a breathing tube. Withdrawal after daily use caused anxiety, irritability or agitation, insomnia and psychosis, and 69.6% needed several medicines. 48.7% of toxicity cases intubated (Not applicable) Methods, limits and fundingOutcomes: Symptoms, treatment and hospital outcomes Limitations: Case reports only, so it cannot say how common these problems are. Funding and conflicts: The authors report no conflicts of interest. Read: abstract |
| de Bie 2023 Effects of gamma-aminobutyric acid supplementation on glucose control in adults with prediabetes: A double-blind, randomized, placebo-controlled trial. Am J Clin Nutr · PMID 37495019 · DOI |
Randomised controlled trial |
52 52 adults aged 50 to 70 with prediabetes and a body mass index of 25 or more. |
Pure GABA capsules (oral) Oral 500 mg three times daily 95 days · vs Placebo |
GABA did not change the blood glucose response after the sugar drink test. After correcting for chance findings, no other measure (including the GABA level in blood, blood pressure and self-reported sleep quality) changed at group level. Difference 0.21 mmol/L (95% CI -0.252 to 0.674; P = 0.364) Methods, limits and fundingOutcomes: Blood glucose response after a sugar drink test; secondary: HbA1c, insulin, blood pressure, blood fats, self-reported sleep quality Limitations: Only people with prediabetes were studied, and the trial was small. The authors say other groups, such as people with advanced diabetes, could be studied. Funding and conflicts: Funding not stated in the abstract. Wageningen University & Research authors. Registration: NCT04303468 Read: abstract |
What we do not know yet
- No trial of standard GABA capsules for stress or sleep, run by researchers with no tie to a maker, was found.
- No brain-scan study of brain GABA after an oral dose was found.
- No trial or review of oral GABA in a diagnosed anxiety disorder was found.
- No long-term safety study and no data in pregnancy, breastfeeding or children were found.
- No study compared GABA capsules with GABA in fermented foods.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Other 3
Self-reported sleep quality
No clear change with GABA in trials
How well people say they slept, on a questionnaire.
Very low certaintyResults and what it means
Why it was measured
To see whether GABA changes sleep.
Statistical vs. clinical meaning
A minor secondary measure in a trial built to test blood glucose. It does not show GABA fails to help sleep problems.
Safety implication
None reported in the abstract.
| Study | Result | People | Product |
|---|---|---|---|
| 10 | No significant effect on any secondary measure, including self-reported sleep quality, after correcting for false discoveries. | 52 adults aged 50 to 70 with prediabetes | GABA capsules for 95 days vs placebo |
Systolic blood pressure
Lower with GABA fermented milk than placebo in one trial; no change with capsules in another in trials
The top number in a blood pressure reading, measured when the heart pushes blood out.
Very low certaintyResults and what it means
Why it was measured
To see whether GABA changes blood pressure.
Statistical vs. clinical meaning
A fermented-milk result that was not repeated with capsules. It does not show GABA treats high blood pressure.
Safety implication
A drop in blood pressure could add to the effect of blood pressure medicine (see the Safety tab).
| Study | Result | People | Product |
|---|---|---|---|
| 5 | -17.4 mmHg from baseline after 12 weeks (SD 4.3); the systolic pressure differed from placebo (P < 0.05) | 39 adults with mild high blood pressure | GABA fermented milk vs placebo for 12 weeks |
| 10 | No significant effect on blood pressure at group level after correcting for false discoveries | 52 adults aged 50 to 70 with prediabetes | GABA capsules for 95 days vs placebo |
Blood glucose after a sugar drink test
No difference from placebo in trials
How high blood glucose rises after a standard sugar drink (an oral glucose tolerance test).
Low certaintyResults and what it means
Why it was measured
To see whether GABA improves how the body handles sugar.
Statistical vs. clinical meaning
The main outcome of the trial; a clear null result in this group.
Safety implication
None reported in the abstract.
| Study | Result | People | Product |
|---|---|---|---|
| 10 | Difference 0.21 mmol/L (95% CI -0.252 to 0.674; P = 0.364) | 52 adults aged 50 to 70 with prediabetes | GABA capsules for 95 days vs placebo |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 3
- Phenibut is not GABA, and it can be dangerous. Phenibut is a GABA look-alike drug sold online as a calming or sleep product. The US Food and Drug Administration (FDA) said in 2019 that phenibut does not meet the definition of a dietary ingredient and that products labelled as supplements that list it are misbranded. A review of 62 reported cases found toxicity with altered mental status, sleepiness and psychosis, and 48.7% of the toxicity cases needed a breathing tube. Withdrawal after daily use caused anxiety, agitation, insomnia and psychosis. A review of 25 withdrawal cases found seizures in 8%, a breathing tube in 24% and intensive care in 44%. If a product lists phenibut, it is not a GABA supplement. Regulator notice and systematic reviews of case reports 8 9 3 7
- GABA itself: no serious events in the studies reviewed, but a small drop in blood pressure. The USP safety review found no serious adverse events at the intakes studied, which included a short high-intake study and a 12-week study. No case reports of adverse events were found. Some studies showed a short, moderate drop in blood pressure (under 10%). The review says GABA taken with blood pressure medicine could conceivably raise the risk of low blood pressure. This is a theory from small studies, not a proven interaction. Safety review of clinical studies and animal data 6
- Pregnancy and breastfeeding: no data, and caution is advised. The USP review found no studies of GABA in pregnancy or breastfeeding. It advised caution because GABA can affect neurotransmitters and hormones, with rises in growth hormone and prolactin seen. Ask a doctor first. Safety review (no human data) 6
Side effects 3
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Short, moderate drop in blood pressure Matters most for people who already take blood pressure medicine. | Seen in some studies as a change of under 10% that did not last. The 95-day capsule trial in prediabetes found no change at group level. | Mild to moderate in the studies reviewed Transient according to the review | Safety review of clinical studies 6 10 |
| Serious adverse events Absence of reports in short studies does not rule out risks with long-term use or in special groups. | None were reported in the studies USP reviewed, and no case reports or spontaneous reports of adverse events were found. | Not applicable Not applicable | Safety review of clinical studies 6 |
| Changes in growth hormone and prolactin This is the reason USP gives for caution in pregnancy and breastfeeding. | The review notes GABA can raise growth hormone and prolactin levels; no numbers are given in the abstract. | Not specified Not specified | Safety review 6 |
Liver
No liver injury from GABA was described in the USP safety review abstract, and no case reports of adverse events were found. The LiverTox database was not checked for this page. 6
How often. No frequency found.
Monitoring. No agency monitoring advice found.
This is a safety connection. It is not evidence that GABA Supplements supports liver health.
Medicines and supplements 3
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Blood pressure medicines prescription | Proposed by the USP review: GABA was linked to a small, short drop in blood pressure, so it could add to the effect of the medicine. | A theoretical risk of low blood pressure. No trial tested GABA with blood pressure medicine. | Safety review reasoning from small studies (no interaction trial) Very low certainty 6 | Ask the prescriber or a pharmacist before adding GABA. |
| Sedatives, sleeping pills and alcohol prescription and non-prescription | GABA calms nerve activity, so a combined sleepy effect is plausible. This is a caution, not a finding. | No study of GABA with sedatives or alcohol was found in the sources read. Among phenibut cases (a different drug), 63.2% also used other addictive substances, mostly benzodiazepines and alcohol. | No data on GABA; case reports for phenibut only Not enough evidence 9 | Ask a pharmacist before combining anything sold for sleep or calm with sedatives or alcohol. |
| Phenibut, baclofen and other GABA-like drugs prescription and non-prescription | These drugs act on GABA receptors. GABA taken by mouth is a different substance, and no study of the combination was found. | Not studied. Phenibut and baclofen are covered here only because phenibut products are often confused with GABA. | No data Not enough evidence 3 | Ask a doctor or pharmacist. |
Who should check first 6
| Situation | Advice | Evidence |
|---|---|---|
| Taking blood pressure medicine, or having low blood pressure | GABA was linked to a small, short fall in blood pressure. Ask the prescriber or a pharmacist first. | Safety review 6 |
| Pregnancy | No studies exist, and USP advised caution. Ask a doctor. | Safety review (no data) 6 |
| Breastfeeding | No studies exist, and USP advised caution. Ask a doctor. | Safety review (no data) 6 |
| Children | No guidance for children was found in the sources read. Ask a doctor. | No data found |
| Kidney or liver disease, and before surgery | Not described in the sources read. Ask a doctor or pharmacist. | No data found |
| Allergy to milk or soy | The USP review notes that some GABA in studies came from fermented milk or soy products. Check any food or supplement label and ask a pharmacist if you have an allergy. | Safety review (product source) 6 |
Overdose, product quality and regulators
Summary. In the animal studies USP reviewed, GABA showed no signs of toxicity. No human overdose cases of GABA were found. Phenibut, a different drug, causes serious toxicity.
Animal. Rats and dogs given GABA for a long time at up to 1 g per kg a day showed no signs of toxicity.
High dose or long term signals. A short high-intake study found no serious adverse events. Long-term use in people has not been studied in the sources read.
Overdose response. No overdose reports for GABA were found. For phenibut, see the key warning.
Genotoxicity. Not researched.
No survey of what is in GABA capsules was read, so purity and label accuracy for GABA products are unknown. Testing of phenibut products shows labels cannot be trusted for that drug.
Phenibut products. In a test of four brands of supplements that listed phenibut, two contained it before the FDA warnings and all four after. Amounts rose in three of four, up to 450% more than a typical 250 mg Russian tablet. 2
GABA products. No testing of GABA capsule contents was found in the sources read.
| Body | Action | Date |
|---|---|---|
| US Food and Drug Administration (Human Foods Program), constituent update (United States) | Issued warning letters to three companies on April 10, 2019 over products labelled as dietary supplements that list phenibut. Said phenibut does not meet the definition of a dietary ingredient and such products are misbranded. This is about phenibut, not GABA. source | 2019-04-16 |
| US Pharmacopeia (USP) safety review of GABA, published in Nutrients (United States) | Found no serious adverse events at the intakes studied; noted a short drop in blood pressure; said GABA with blood pressure medicine could conceivably raise the risk of low blood pressure; advised caution in pregnant and breastfeeding women. source | 2021-08-10 |
When to get medical help
- Very drowsy, confused, hard to wake, or trouble breathing after taking a calming or sleep product, especially one that may contain phenibut: call emergency services at once. In the US, Poison Help is 1-800-222-1222.
- After stopping daily phenibut: hallucinations, seizures, severe agitation or confusion are emergencies. Get urgent medical help instead of trying to stop alone.
- Rash, swelling of the face or throat, or trouble breathing after any supplement: get urgent medical help.
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What is GABA?
GABA (gamma-aminobutyric acid) is the main calming chemical messenger in the brain. The body makes it, and some foods and supplements contain it.
Does GABA taken by mouth reach the brain?
Not established. Studies on whether it crosses the blood-brain barrier are contradictory, and a 2015 review called for brain measurements in people.
Does GABA help with stress?
Limited evidence. A systematic review of 14 trials found limited evidence for stress benefits, using GABA from foods or fermentation.
Does GABA help with sleep?
Does GABA help anxiety disorders?
We found no trial or review of oral GABA in people with a diagnosed anxiety disorder. Lasting anxiety deserves a proper assessment.
Is GABA safe?
The USP safety review found no serious adverse events in the studies it examined, but the studies were short and mostly small. It noted a small, short drop in blood pressure.
Can GABA lower blood pressure?
Is GABA safe in pregnancy or breastfeeding?
No studies exist. The USP review advised caution because GABA can affect hormones such as growth hormone and prolactin. Ask a doctor first.
Is phenibut a form of GABA?
Why is phenibut dangerous?
Does GABA help control blood sugar?
A 95-day trial in 52 adults with prediabetes found no change in blood glucose after a sugar drink test.
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Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We started from our existing summary and re-read the PubMed abstracts for the reviews and trials, plus the FDA page on phenibut. Only abstracts were read for studies. The NIH Office of Dietary Supplements was not checked and is marked unverified.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. We say where an author or study is linked to industry.
Sources 10
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Boonstra E, de Kleijn R, Colzato LS, Alkemade A, Forstmann BU, Nieuwenhuis S. Neurotransmitters as food supplements: the effects of GABA on brain and behavior.. Front Psychol. 2015. PMID 26500584. DOI 10.3389/fpsyg.2015.01520. (abstract)
- Cohen PA, Ellison RR, Travis JC, Gaufberg SV, Gerona R. Quantity of phenibut in dietary supplements before and after FDA warnings.. Clin Toxicol (Phila). 2022. PMID 34550038. DOI 10.1080/15563650.2021.1973020. (abstract)
- Feldman R, Autry B, Dukes J, Lofy T, Marchetti G, Patt A, Batterman N, Theobald J. A systematic review of phenibut withdrawal focusing on complications, therapeutic approaches, and single substance versus polysubstance withdrawal.. Clin Toxicol (Phila). 2023. PMID 38112312. DOI 10.1080/15563650.2023.2285702. (abstract)
- Hepsomali P, Groeger JA, Nishihira J, Scholey A. Effects of Oral Gamma-Aminobutyric Acid (GABA) Administration on Stress and Sleep in Humans: A Systematic Review.. Front Neurosci. 2020. PMID 33041752. DOI 10.3389/fnins.2020.00923. (abstract)
- Inoue K, Shirai T, Ochiai H, Kasao M, Hayakawa K, Kimura M, Sansawa 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. DOI 10.1038/sj.ejcn.1601555. (abstract)
- Oketch-Rabah HA, Madden EF, Roe AL, Betz JM. United States Pharmacopeia (USP) Safety Review of Gamma-Aminobutyric Acid (GABA).. Nutrients. 2021. PMID 34444905. DOI 10.3390/nu13082742. (abstract)
- Penzak SR, Bulloch M. Phenibut: Review and Pharmacologic Approaches to Treating Withdrawal.. J Clin Pharmacol. 2024. PMID 38339875. DOI 10.1002/jcph.2414. (abstract)
- U.S. Food and Drug Administration. FDA Acts on Dietary Supplements Containing DMHA and Phenibut (HFP Constituent Update). FDA Human Foods Program constituent update, April 16, 2019. 2019. (page text, 2026-10-26)
- Weleff J, Kovacevich A, Burson J, Nero N, Anand A. Clinical Presentations and Treatment of Phenibut Toxicity and Withdrawal: A Systematic Literature Review.. J Addict Med. 2023. PMID 37579098. DOI 10.1097/ADM.0000000000001141. (abstract)
- de Bie TH, Witkamp RF, Balvers MG, Jongsma MA. Effects of gamma-aminobutyric acid supplementation on glucose control in adults with prediabetes: A double-blind, randomized, placebo-controlled trial.. Am J Clin Nutr. 2023. PMID 37495019. DOI 10.1016/j.ajcnut.2023.07.017. (abstract)
Where to buy
Check the label first. Whatever you buy, look for these:
- The amount of the active ingredient per serving, not just the front-label claim
- A third-party testing mark (USP, NSF or ConsumerLab)
- Other ingredients and allergens
- Ask a pharmacist about interactions with your medicines
Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.
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