GABA: Benefits, Forms, Dosing, and Side Effects

Table of Contents

• Current evidence position
• Key safety points
• Brad's videos on this topic
• Overview
• Forms and Bioavailability
• Evidence for Benefits
• Recommended Dosing
• Safety and Side Effects
• Drug Interactions
• Dietary Sources
• References

Current evidence position

Brad has not made a video on this topic; this is a summary of the evidence, not his view. A 2020 systematic review of 14 placebo-controlled trials found limited evidence for stress and very limited evidence for sleep benefits of oral GABA, and it is still unclear whether GABA taken by mouth reaches the brain ^{[5, 7]}. In small trials, 100 to 300 mg of GABA (as capsules or an extract of fermented rice germ) taken for 1 to 4 weeks shortened the time to fall asleep, but most other sleep measures did not change ^{[5, 12]}. Food-based products providing GABA, such as a GABA-rich chlorella supplement giving 20 mg of GABA twice a day, modestly lowered systolic blood pressure when taken for 12 weeks ^{[19, 20]}. A safety review found no serious side effects in studies of up to 12 weeks, but since GABA may reduce blood pressure, people taking blood pressure medicines, and people who are pregnant or breastfeeding, should talk to their doctor first ^[28].

Brad's videos on this topic

None yet.

1. Overview

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mammalian cortex: it damps down nerve-cell activity and balances glutamate, the main excitatory neurotransmitter ^[3]. The brain makes GABA from glutamate and can recycle it back into glutamate through the tricarboxylic acid cycle ^[3].

GABA acts through two main receptor types. GABA_A receptors are chloride channels that mediate inhibitory signalling ^[4]. GABA_B receptors act more slowly, through G proteins.

Several medicines act on this system. Benzodiazepines increase the binding of GABA to GABA_A receptors ^[12]. Gabapentin, an epilepsy drug designed to mimic GABA, raised brain GABA levels in a brain-scan study of people with epilepsy ^[14].

The problem with oral GABA is getting it into the brain. It has long been thought that GABA cannot cross the blood-brain barrier, but the studies on this question disagree and use very different methods ^[7].

GABA also occurs naturally in foods ^[5]. One review suggests that any real effects of GABA supplements might come from GABA crossing the barrier or, more indirectly, from an effect on the gut's own nerves (the enteric nervous system) ^[7].

People with major depression have lower brain GABA levels ^[6]. A GABA shortfall in a condition does not mean oral GABA can correct it: the medicines above act directly in the brain.

2. Forms and Bioavailability

Types of GABA Supplements

GABA supplements are made in several ways:

Biosynthetic GABA: GABA produced by fermentation ^[5].

Synthetic GABA: Made by chemical synthesis. It is the same molecule as biosynthetic GABA.

Natural GABA from fermented foods: GABA present naturally in foods ^[5]. Trials have used a fermented milk ^[19], a GABA-rich chlorella ^[20] and an extract of fermented rice germ ^[12].

GABA in combination products: A blend's effects cannot be credited to GABA alone.

Supplement Delivery Forms

GABA comes as capsules, tablets, powders and liquids. In short studies of large doses (5 g or 10 g a day), a few people felt a slight burning sensation in the throat that passed within minutes ^[28].

Blood-Brain Barrier Penetration

The central question is whether GABA taken by mouth reaches the brain in useful amounts. The evidence is mixed:

• It has long been thought that GABA cannot cross the blood-brain barrier, but studies of this question are contradictory ^[7].
• In an old study, very large GABA doses (0.8 g/kg daily) reduced seizures in only 4 of 12 people with epilepsy ^[7].
• A 2020 systematic review noted that it is not known whether oral GABA raises brain GABA levels ^[5].

However, there are caveats:

• All of the people who responded in that epilepsy study were children below the age of 15, which fits the idea that the barrier lets less GABA through with age ^[7].
• There is evidence of a GABA transporter in the barrier ^[7].
• Some effects of GABA, such as on blood pressure, may not need it to reach the brain; one review raises the gut's nerves as another route ^[7].

Absorption and Pharmacokinetics

GABA is quickly absorbed. In one study, blood GABA was highest 30 minutes after an oral dose and then fell ^[8]. This fast rise and fall may explain why trials gave GABA shortly before the effect was wanted ^{[8, 10]}.

Vitamin B6 Dependency

The enzyme that makes GABA from glutamate, glutamic acid decarboxylase, needs pyridoxal 5'-phosphate, the active form of vitamin B6.

3. Evidence for Benefits

Stress and Anxiety

Trials suggest GABA may change brain-wave (EEG) markers linked to relaxation, but most were small and many were run by researchers with a potential conflict of interest ^{[5, 7]}.

Alpha and beta brain wave effects: In a study of 13 people, GABA raised alpha waves and lowered beta waves on EEG 60 minutes after intake, compared with water or L-theanine ^[9]. The authors read this as a sign of relaxation and less anxiety ^[9].

Mental stress testing: In a single-blind crossover trial in 63 adults, mental stress tasks reduced alpha and beta waves. Thirty minutes after 100 mg GABA capsules, this fall was smaller than after placebo, and mood scores on the POMS questionnaire matched this ^[10].

Systematic review conclusion: A 2020 review of 14 placebo-controlled studies of natural or biosynthetic GABA concluded that "there is limited evidence for stress and very limited evidence for sleep benefits of oral GABA intake" ^[5].

Neuroimaging context: Brain-scan studies have found lower brain GABA in major depression ^[6]. These findings concern GABA made in the brain, which oral supplements may not reach.

Sleep and Insomnia

Sleep medicines such as benzodiazepines work by boosting GABA's action at GABA_A receptors ^[12]. Trials of GABA itself for sleep are few and small ^[5].

Fermented rice germ extract (300 mg GABA): A trial gave 300 mg of GABA from a rice germ extract, or placebo, daily for 4 weeks to 40 adults with insomnia symptoms (30 on GABA, 10 on placebo) ^[12]. In the GABA group, time to fall asleep fell from 13.4 to 5.7 minutes and sleep efficacy rose from 79.4% to 86.1% ^[12]. Only the time to fall asleep differed between the groups, and the placebo group was small ^[12].

GABA capsules (100 mg): In a 1-week crossover study, 100 mg GABA capsules shortened the time to fall asleep, measured by EEG, and increased total non-REM sleep ^{[5, 8]}. They did not change deep sleep, REM sleep time or how often people woke ^[5].

GABA with exercise (200 mg): A trial in 30 sedentary women with overweight or obesity gave 200 mg of GABA or placebo daily for 90 days while both groups exercised ^[13]. The GABA group improved its habitual sleep efficiency on the Pittsburgh Sleep Quality Index, and its depression scores and heart-rate variability ^[13].

GABAergic signaling and sleep physiology: Brain GABA systems help control sleep, and benzodiazepine sleep medicines act on them ^[12]. The small effects of oral GABA fit the doubt that much of it reaches the brain.

Summary: The evidence for GABA and sleep is weak. Doses of 100 to 300 mg for 1 to 4 weeks may shorten the time to fall asleep, but there is little evidence for better sleep quality, longer sleep or fewer awakenings ^{[5, 12]}.

Epilepsy

Many epilepsy drugs work on the GABA system, and the epilepsy drug gabapentin raised brain GABA in a brain-scan study ^[14].

High-dose study: In an old study, very large GABA doses (0.8 g/kg daily) reduced seizures in only 4 of 12 people with epilepsy, all of them children below the age of 15 ^[7]. The response in children fits the idea that the blood-brain barrier lets less GABA through with age ^[7].

Summary: The only evidence is one small, old study, and it does not show that GABA helps epilepsy ^[7].

Cognitive Function

In 24 older people with subjective cognitive decline or mild cognitive impairment, groups at high risk of Alzheimer's disease, higher GABA levels in the prefrontal cortex went with better memory scores ^[15]. Trials of oral GABA for thinking are few and limited to single doses in young adults.

Positive findings: In a randomised, placebo-controlled experiment in young healthy adults, GABA improved some measures of temporal attention (fewer order errors) but did not change spatial attention ^[17]. A 2015 trial that reported better action selection after 800 mg of GABA was later retracted ^[16], and two of its authors also wrote the attention study ^[17].

Negative finding: In a trial of 48 healthy volunteers split into four groups, GABA alone, and GABA with tyrosine, worsened task switching, a measure of cognitive flexibility ^[18].

Summary: Results are mixed and come from short, single-dose studies in young healthy adults. There are no long-term trials, and no good evidence supports GABA for memory or thinking.

Blood Pressure (Hypertension)

Small trials of GABA-containing foods found modest falls in systolic blood pressure; a safety review describes the effect as a transient and moderate drop (less than 10% change) ^[28].

Fermented milk product: In a single-blind trial in 39 mildly hypertensive patients, systolic blood pressure fell by a mean of 17.4 mmHg from baseline after 12 weeks of a GABA-containing fermented milk, and differed from placebo; diastolic pressure fell by 7.2 mmHg from baseline ^[19].

Chlorella supplement (20 mg GABA twice daily): In a double-blind trial in 80 people with high-normal blood pressure or borderline hypertension, GABA-rich chlorella, taken twice a day for 12 weeks at 20 mg GABA per dose, lowered systolic blood pressure more than placebo, with a larger fall in borderline hypertension ^[20]. Diastolic pressure only tended to fall, and no adverse events were reported ^[20].

Summary: Small trials suggest that GABA from food-based products may modestly lower systolic pressure when blood pressure is mildly raised ^{[19, 20, 28]}.

Muscle Building and Growth Hormone

GABA raised growth hormone levels in some studies, so it has been tested for muscle gain with resistance training ^{[21, 22]}.

Growth hormone release: In a crossover trial in 11 resistance-trained men, 3 g of GABA raised peak growth hormone at rest by about 400% compared with placebo ^[21]. Thirty minutes after intake, growth hormone was 200% higher with GABA plus exercise than with placebo plus exercise ^[21].

Muscle mass with whey protein: In a trial in 21 healthy men doing resistance training twice a week, 100 mg of GABA with 10 g of whey protein daily for 12 weeks led to a larger gain in whole-body fat-free mass than whey alone ^[22]. Resting growth hormone rose at 4 and 8 weeks from baseline in the GABA group, and only at 8 weeks in the whey-only group ^[22].

Negative findings in women: In a trial in 26 women with obesity who exercised 3 days a week, 200 mg GABA a day for 90 days made no difference compared with placebo to growth hormone, body fat, fat-free mass, blood pressure or heart rate ^[23]. Sit-up performance improved only in the GABA group ^[23]. This trial and the sleep trial above ^[13] share authors and a design, so they probably report one trial.

Summary: A single 3 g dose may briefly raise growth hormone. One trial found more fat-free mass with GABA plus whey protein, but a trial in women found no difference from placebo in growth hormone or body composition ^{[21, 22, 23]}.

Restless Legs Syndrome (RLS)

In a brain-scan study, GABA levels were no different between 18 people with RLS and matched controls, though higher thalamic GABA and lower cerebellar GABA went with more severe symptoms ^[24]. Gabapentin and pregabalin, medicines related to GABA, are recommended for RLS by the American Academy of Sleep Medicine ^[30]. GABA supplements have not been shown to help RLS.

Gut-Brain Axis and Microbiome

One review suggests that GABA supplements, if they have real effects, might act through the gut's own nervous system rather than by reaching the brain ^[7]. This idea has not been tested in clinical trials.

Pancreatic Function and Blood Sugar

Whether oral GABA affects blood sugar control in people has not been established.

Immune Modulation

In a tiny study, people afraid of heights who took GABA kept higher saliva levels of immunoglobulin A (an antibody) while crossing a suspension bridge than those given placebo ^[9]. There is no clinical evidence that GABA helps inflammatory or autoimmune disease.

4. Recommended Dosing

Doses in clinical studies range widely, and their effects were modest:

Dosing by Indication

General Dosing Guidance

• Timing: Blood GABA peaks about 30 minutes after a dose and then falls ^[8]. In a stress study, effects were seen 30 minutes after intake ^[10].
• High-dose precaution: A few people felt a slight burning sensation in the throat after large doses (5 g or 10 g a day), which passed within minutes ^[28].

Important Context

The evidence for GABA at any dose is limited. A systematic review rated the stress evidence as limited and the sleep evidence as weaker still ^[5]. Even positive trials found small effects that may not matter in daily life, and oral GABA may not reach the brain at all ^[7].

5. Safety and Side Effects

General Safety Profile

A 2021 safety review found no serious adverse events with GABA at intakes up to 18 g a day for 4 days, or 120 mg a day for 12 weeks, and no case reports of harm ^[28]. In rats and dogs, GABA at up to 1 g/kg a day over long periods showed no signs of toxicity ^[28].

Reported Side Effects

Reported side effects were mild to moderate ^{[12, 28]}:

• Abdominal discomfort: 2 of 30 people taking 300 mg of GABA a day ^[12]
• Headache: 1 of 30 people taking 300 mg a day ^[12]
• Drowsiness: 1 of 30 people taking 300 mg a day, and 1 person on placebo ^[12]
• Throat irritation: a slight burning sensation in the throat after large doses (5 g or 10 g a day), which passed within minutes ^[28]

Long-Term Safety

The longer studies in the 2021 safety review ran for 12 weeks, at 120 mg a day, with no serious adverse events ^[28].

Pregnancy and Fertility

No studies have tested GABA in pregnancy or breastfeeding ^[28]. A safety review advises caution because GABA can affect neurotransmitters and hormones, raising growth hormone and prolactin ^[28]. A mouse study adds to the concern:

• High-dose oral GABA (12.5 mg/g, about 12.5 g/kg, far above supplement doses) given to pregnant mice before implantation reduced the number of implantation sites, and most unimplanted embryos were degenerated or underdeveloped ^[29].
• Markers of a receptive womb lining (LIF, E-cadherin and HOXA10) fell ^[29].
• In the lab, GABA at 10 to 50 μg/μL slowed early embryo development as the dose rose, through GABA_B receptors ^[29].

The authors concluded that these findings could raise concerns about GABA during early pregnancy ^[29]. With no human safety data and these animal findings, avoid GABA during pregnancy, while trying to conceive, or while breastfeeding unless your doctor advises it ^{[28, 29]}.

Alcohol Interaction

Alcohol also acts on GABA_A receptors, so combining it with GABA could, in theory, add to drowsiness. This has not been studied with GABA supplements.

6. Drug Interactions

Blood Pressure Medications

Because GABA lowered blood pressure in some studies, a safety review considers it conceivable that GABA could interact with blood pressure medicines, such as propranolol and metoprolol, and increase the risk of low blood pressure ^[28]. Low blood pressure can cause dizziness or falls, especially in older people.

SSRIs and Antidepressants

If you take prescription medicines, check with your doctor or pharmacist before starting.

Benzodiazepines and Sedatives

Benzodiazepines increase the binding of GABA to GABA_A receptors ^[12]. Taking GABA with them, or with zolpidem or other sleep medicines, could in theory add to drowsiness. This has not been studied with GABA supplements.

Gabapentin and Pregabalin

Gabapentin was designed to mimic GABA ^[14]. Taking it, or pregabalin, with GABA supplements could in theory add to drowsiness.

Antiepileptic Drugs

GABA did not reliably reduce seizures in the one study described above ^[7]. People taking epilepsy medicines should not use GABA in place of them and should ask their doctor before trying it.

Immunosuppressants

If you take immunosuppressant medicines, check with your doctor or pharmacist before starting.

Summary Table

7. Dietary Sources

GABA occurs naturally in foods ^[5], but usually in amounts far smaller than supplement doses. To match the 100 mg dose used in one stress study, you would need to eat 2.34 kg of uncooked spinach, and spinach is relatively rich in GABA ^[7].

Foods Containing GABA

Trials have used foods made to carry more GABA: a fermented milk ^[19], a GABA-rich chlorella ^[20] and an extract of fermented rice germ ^[12]. The GABA content of everyday foods varies widely with the food and how it is prepared.

Fermented Foods and the Gut Microbiome

Whether fermented foods change GABA signalling through the gut in people is unknown; one review raises the gut's own nervous system as a possible route ^[7].

Nutrients Involved in GABA Production

The body makes its own GABA in the brain, where oral GABA may not reach:

• Vitamin B6 (pyridoxine): The active form of vitamin B6 is the cofactor for glutamic acid decarboxylase, the enzyme that turns glutamate into GABA.
• Glutamate/glutamine: Glutamate is the precursor of GABA ^[3]. Protein-rich foods supply it.
• Magnesium: In mice, magnesium's anti-anxiety effect depended on benzodiazepine/GABA_A receptors ^[27].