Glycine: Benefits, Forms, Dosing, and Side Effects

Table of Contents

• Current view (reviewed 20 October 2026)
• 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 view (reviewed 20 October 2026)

In three small trials, 3 g of glycine before bed improved how people rated their sleep, helped them fall asleep faster, and reduced next-day tiredness or sleepiness (Brad's current guidance, 3 Oct 2026). In one of these trials, overnight sleep recordings showed people reached slow-wave sleep sooner with no change in sleep architecture, but no trial reported fewer night-time wake-ups (Brad's current guidance, 3 Oct 2026). For Brad, glycine is about sleep, and he calls the effect real, though modest (Brad, 20 Aug 2025). He considers glycine generally safe at typical doses of about 3 g a day, though his taking a supplement does not mean you should (Brad, 27 May 2025). A placebo-controlled human study found that glycine combined with N-acetylcysteine (GlyNAC) corrected glutathione deficiency in older adults and improved hand grip strength (Brad's current guidance, 31 Jul 2026). Because the benefits in a 2022 GlyNAC study appeared only in older adults, not younger ones, Brad plans to start GlyNAC at age 45 (Brad, 3 Feb 2026).

Brad's videos on this topic

• 3 Feb 2026, The Most Important Antioxidant Study I’ve Ever Read: a new meta-analysis in adults over 55 found antioxidants plus exercise gave small gains in strength and walking; Brad still avoids vitamins A and E and plans to start GlyNAC, a glutathione precursor, at age 45.
• 20 Aug 2025, Glycine was Accidentally Found To Improve Our Sleep: the sleep trials used 3,000 mg shortly before bed, glycine did not change sleep architecture, and Brad calls the effect real but modest.
• 30 Jul 2025, The Only Three Supplements Doctor Brad Takes: Brad takes glycine at bedtime because studies found it improved sleep quality, deep sleep and next-day memory performance without disrupting sleep architecture.
• 27 May 2025, Doctor Reveals Why He Takes Glycine Every Day: Brad takes glycine for sleep, citing small trials and a strong safety profile; he rates the evidence for metabolic health as good and the heart, brain and mouse lifespan findings as early.

1. Overview

Glycine is the simplest amino acid, and a major one in humans and other mammals ^{[51, 52]}. Unlike all other standard amino acids, glycine is the only achiral proteinogenic amino acid — it has no stereogenic center, meaning there are no L- or D- forms. The body uses it to make glutathione, creatine, heme and other compounds, and it has roles in antioxidant defence and nerve signalling ^[51].

Glycine synthesis in the body supplies about 3 g a day ^[4], mainly in the liver and kidneys, from serine, threonine and other precursors ^[51].

Because the body can make it, glycine is classed as non-essential ^[52]. However, some research suggests it is conditionally essential, because the body may not make enough for collagen, glutathione, creatine, bile acids and its other uses ^{[4, 51]}. One analysis estimated that the body makes about 3 g a day and the diet supplies 1.5 to 3.0 g a day, which may fall short of the amount needed for all metabolic uses, including collagen synthesis, by about 10 g a day for a 70 kg adult ^[4].

Glycine acts as both an inhibitory neurotransmitter and an excitatory co-agonist in the central nervous system. As an inhibitory neurotransmitter, it helps process the motor and sensory signals behind movement, vision and hearing ^[7]. Glycine also strengthens the action of glutamate at the N-methyl-D-aspartate (NMDA) receptor, which needs glycine as a co-agonist to work ^{[7, 22]}. This NMDA action has been proposed to explain glycine's effects on sleep ^[13] and on schizophrenia symptoms ^[22].

The body also needs glycine to make collagen ^[4]. A review lists glycine as a building block for glutathione, heme, creatine, nucleic acids and uric acid, and as a part of the bile acids that help digest fat ^[51].

Food adds about 1.5 to 3.0 g a day ^[4].

Most human trials of glycine are small. Researchers at Ajinomoto, a glycine maker, ran at least one of the sleep studies ^[17], and another enrolled Ajinomoto employees ^[16]; other trials tested glycine for bladder symptoms and schizophrenia.

2. Forms and Bioavailability

Supplemental Forms

Glycine supplements are available in several delivery formats:

Key Purchasing Considerations

Glycine comes in only one form, because it has no L- or D- version (see Overview). A label claim such as "free form" or "biologically active" adds nothing: every glycine supplement supplies the same molecule.

Stability and Storage

Glycine is heat-stable, so it can be mixed into hot drinks such as coffee and tea ^[9]. Keep the container closed somewhere cool and dry, and leave any desiccant pack inside to keep moisture out.

Calorie Content

Like other amino acids, glycine supplies some energy, but a few grams a day adds few calories.

Bioavailability

Free-form glycine is rapidly absorbed from the gastrointestinal tract. As the simplest amino acid, it does not require enzymatic digestion before absorption and is transported across intestinal epithelial cells via active amino acid transport systems.

When glycine is chelated to minerals (as in magnesium glycinate), the glycine component is released during digestion and contributes to the body's glycine pool.

3. Evidence for Benefits

Sleep and Fatigue

Glycine's effects on sleep are among the best-studied benefits of supplementation. The proposed mechanism centres on the suprachiasmatic nucleus (SCN), the brain's body clock. Rat studies suggest that glycine acts on NMDA receptors in the SCN, widens blood vessels in the skin and lowers core body temperature, which may help sleep begin ^{[13, 14]}.

Clinical trial 1, Yamadera et al. (2007): In 11 adults unhappy with their sleep, 3 grams of glycine one hour before bed improved how they rated their sleep compared with placebo. Overnight recordings of brain waves, heart rate and breathing (polysomnography) showed they fell asleep faster and reached deep (slow-wave) sleep sooner ^[15].

Clinical trial 2, Inagawa et al. (2006): In 15 Ajinomoto employees dissatisfied with their sleep, 3 grams of glycine one hour before bed improved rated sleep quality compared with placebo. They felt more refreshed on waking and less tired during the day ^[16].

Clinical trial 3, Bannai et al. (2012): In healthy volunteers whose sleep was cut by 25% for three nights, 3 g of glycine before bed reduced next-day fatigue and tended to reduce sleepiness compared with placebo. They also did better on a psychomotor vigilance test the next day ^[17].

Mechanism — core body temperature: Kawai et al. (2015) demonstrated in animal models that glycine's sleep-promoting and hypothermic effects are mediated by NMDA receptors in the suprachiasmatic nucleus ^[13]. The hypothermic response — a lowering of core body temperature — is a critical physiological signal for sleep initiation. This mechanism is distinct from that of sedative drugs, which suppress neural activity rather than facilitating the body's natural thermoregulatory sleep signals. This means glycine promotes sleep through a natural physiological pathway rather than through pharmacological sedation, which is consistent with the clinical finding that glycine does not cause next-morning grogginess ^{[13, 14]}.

All three clinical trials were small and short-term, and researchers at Ajinomoto, which makes glycine, ran at least one of them ^[17]. While the consistent direction of results across the three trials is encouraging, larger independent trials are needed to strengthen the evidence base.

Overactive Bladder

Sugaya et al. (2021) studied 20 urology outpatients (16 men and four women) with overactive bladder symptoms ^[18]. During the glycine phase, each took 3 g twice a day (6 g a day in total) for four weeks ^[18].

The published report describes all participants taking a glucose placebo for the first four weeks and then glycine for the next four weeks, rather than random assignment ^[18].

Results:

• Compared with the placebo phase, glycine reduced night-time urination, urgency and urine storage symptom scores ^[18]
• Sleep latency, bladder pain and blood pressure also improved during the glycine phase ^[18]
• The placebo phase itself improved some symptoms, including urinary frequency ^[18]
• There were no adverse events ^[18]

Even so, the 2024 American Urological Association guideline on overactive bladder finds too little evidence to recommend a supplement, vitamin or nutraceutical for its symptoms ^[19]. The study was small (n=20) and short (1 month), limiting the strength of conclusions that can be drawn.

Schizophrenia

Small trials suggest glycine may help some people with schizophrenia, possibly by boosting NMDA receptor signalling. The NMDA receptor hypofunction hypothesis of schizophrenia proposes that reduced NMDA receptor signaling contributes to the negative symptoms of the disease (emotional withdrawal, reduced motivation, social withdrawal) ^{[20, 22]}.

Heresco-Levy et al. (2004): In a double-blind, placebo-controlled crossover trial in 17 people with schizophrenia taking olanzapine or risperidone, adding 0.8 g/kg of glycine a day for 6 weeks gave these results ^[21]:

• Negative symptoms fell significantly, by 23% ^[21]
• Cognitive and positive symptoms also improved significantly ^[21]

The published trial reported that glycine was well tolerated, and its authors suggested that olanzapine and risperidone may act on NMDA receptors differently from clozapine ^[21].

Heresco-Levy et al. (1999): An earlier double-blind, placebo-controlled crossover trial in 22 treatment-resistant patients added 0.8 g/kg of glycine a day to their medicine for 6 weeks ^[22].

The published trial reported a 30% reduction in negative symptoms ^[22].

A separate study in 12 people found a 34% reduction in negative symptoms, without significant changes in serum antipsychotic levels ^[8].

Clozapine interaction, Potkin et al. (1999): In a small double-blind trial, glycine added to clozapine (Clozaril) did not help, and the authors suggested glycine may interfere with clozapine's antipsychotic effect ^[23]. This finding means that while glycine may be a useful adjunct to some antipsychotic medications (olanzapine, risperidone), it should NOT be combined with clozapine, as it may worsen outcomes.

Summary: High-dose glycine (0.8 g/kg/day) may modestly reduce negative symptoms of schizophrenia when used as an adjunct to non-clozapine antipsychotics. The doses required are very large and may cause gastrointestinal side effects. This application should only be pursued under specialist psychiatric supervision.

Depression

Glycine has been proposed as a possible help for depression, but this remains unproven.

Observational evidence: Altamura et al. (1995) found significantly lower plasma glycine in unmedicated people with major depression than in healthy controls ^[24]. Plasma glycine levels are also lower in people with metabolic syndrome than in healthy people ^[46].

Preclinical evidence: Laboratory studies have found mechanisms by which glycine could influence mood ^[26]:

• Laboute et al. (2023) reported in Science that the receptor GPR158 responds to glycine and regulates the excitability of brain cells, with possible implications for mood and thinking ^[26]

Clinical data: The trial evidence is indirect. In the Heresco-Levy et al. (1999) schizophrenia trial, the improvement in negative symptoms was unrelated to changes in depression symptoms ^[22].

Conclusion: The mechanistic rationale exists, and the observational association between low glycine levels and depression is consistent, but there is insufficient interventional evidence to recommend glycine supplementation specifically for depression.

Glutathione and Antioxidant Support

The body uses glycine to make glutathione (GSH), an important antioxidant ^[51].

GlyNAC supplementation: GlyNAC combines glycine with N-acetylcysteine (NAC). In an open-label pilot trial, 8 older adults took GlyNAC for 24 weeks. It corrected red blood cell glutathione deficiency, oxidative stress and mitochondrial dysfunction, and improved inflammation, insulin resistance, strength, gait speed and cognition; the benefits declined after 12 weeks off GlyNAC ^[11]. Research by Kumar et al. at Baylor College of Medicine has shown that GlyNAC supplementation in older adults and in people with HIV corrects age-related glutathione deficits and improves markers of oxidative stress, mitochondrial function, and inflammation.

Human aging data: Human evidence for longevity effects is preliminary, deriving mainly from GlyNAC studies that improve GSH and mitochondrial function without yet demonstrating direct longevity outcomes ^[11].

Anti-inflammatory Effects

Glycine may help regulate immune function ^[50]. A review reported that glycine dampens the activity of several white blood cells, including macrophages, neutrophils and lymphocytes, and that dietary glycine protected rats against endotoxaemia and liver injury after interrupted blood flow (ischaemia-reperfusion) ^[50]. There is limited human clinical evidence for direct anti-inflammatory benefits of glycine supplementation.

Cardiovascular Health

Blood pressure: In the Sugaya et al. (2021) bladder study, blood pressure fell during the glycine phase (3 g twice a day), but everyone took placebo first and glycine second, without randomisation ^[18].

Overall assessment: The cardiovascular evidence for glycine supplementation is largely preclinical. Blood pressure reduction has been observed but not confirmed in placebo-controlled trials. The strongest cardiovascular rationale may be glycine's role in glutathione synthesis and anti-inflammatory signaling.

Blood Sugar and Insulin Sensitivity

Insulin stimulation: In a small randomised, placebo-controlled trial in 12 healthy first-degree relatives of people with type 2 diabetes, a morning dose of 5 g of glycine increased insulin responses without changing insulin action ^[44].

Glucose response: In a small study in healthy people, taking glycine with glucose cut the blood glucose response by more than 50% compared with glucose alone ^[45].

Metabolic syndrome: A review found that plasma glycine levels are lower in people with metabolic syndrome than in healthy people ^[46].

Overall assessment: Long-term supplementation trials for glucose metabolism are insufficient to support specific recommendations.

Collagen Synthesis and Joint Health

The body needs glycine to make collagen ^[4].

Conditional deficiency argument: Meléndez-Hevia et al. (2009) argued through metabolic flux analysis that the amount of glycine synthesized endogenously is insufficient to meet the body's needs for collagen turnover, glutathione production, and other demands — supporting the concept that glycine is conditionally essential ^[4]. It estimated that synthesis supplies about 3 g a day and the diet 1.5 to 3.0 g a day, which may fall short of total needs by about 10 g a day for a 70 kg adult ^[4].

Practical implications: Direct human clinical trials of glycine supplementation for joint health are limited.

Gut Health

This review found no reliable human evidence to cite on glycine and gut health.

Exercise Performance and Recovery

A 2024 literature review reports some evidence that glycine supplementation may enhance peak power output, reduce lactic acid build-up during high-intensity exercise, and improve sleep quality and recovery ^[28]. It concluded that more randomized controlled trials in humans are needed before glycine can be recommended for athletic performance.

Obsessive-Compulsive Disorder (OCD)

Glycine has been investigated as a treatment for OCD because it is an NMDA receptor co-agonist ^[30].

Greenberg et al. (2009): A small double-blind, placebo-controlled trial added glycine, titrated to 60 g a day, for 24 adults with OCD on stable treatment. Many did not keep taking it, mainly because of the taste or nausea, so only 14 could be evaluated. Yale-Brown Obsessive Compulsive Scale (Y-BOCS) scores fell 6.04 points with glycine (n=5) and 1.00 point with placebo (n=9). The weekly difference just missed statistical significance (p=0.053) ^[29].

Case report: A long-term open-label case report described high-dose glycine treatment administered over more than 5 years resulting in robust and sustained reduction of symptoms in a patient with refractory OCD and comorbid body dysmorphic disorder (BDD), with only partial relapses during brief interruptions ^[30].

These findings expand on glycine's psychiatric applications beyond schizophrenia, though evidence remains preliminary and requires confirmation in larger, better-tolerated controlled trials.

Tinnitus

Glycine is sometimes promoted for tinnitus (ringing in the ears) because it calms nerve activity. Animal studies link tinnitus to changes in glycine signalling in hearing pathways ^[31]. Glycine's role as an inhibitory neurotransmitter in auditory pathways provides theoretical rationale, but no clinical evidence supports this use.

Aging and Longevity

Animal models: In the Interventions Testing Program, funded by the U.S. National Institute on Aging, glycine supplementation led to a small but statistically significant lifespan increase in mice of about 4–6% on average across three independent testing sites ^{[42, 48]}. A small earlier study had suggested that glycine could extend lifespan in rats ^[48]. In a mouse study, mice given GlyNAC lived 24% longer than control mice ^[47]. In a lab study, treating skin cells (fibroblasts) from elderly people with glycine prevented age-related defects in mitochondrial respiration ^[49]. Whether these findings apply to humans is unknown.

Human evidence: Human evidence is preliminary, deriving mainly from GlyNAC combination studies that improve glutathione levels, mitochondrial function, and oxidative stress markers without yet demonstrating direct longevity outcomes ^[11]. Larger, longer-duration human trials are needed before making anti-aging recommendations.

4. Recommended Dosing

Dosing by Indication

Practical Dosing Notes

• Most studied dose for sleep: 3 grams taken approximately 1 hour before bedtime. This dose has been consistent across all three sleep trials ^{[15, 16, 17]}.
• Powder versus capsules: At a dose of 3 g/day, powder is more practical than capsules (3 g = 3–6 capsules depending on capsule size). Glycine powder tastes sweet and dissolves in water or hot drinks ^[9].
• Duration: Sleep benefits have been observed within the first few nights in clinical trials. Trials outside sleep used far larger doses, such as 0.8 g/kg a day in schizophrenia ^{[21, 22]}.

Product Mention

Dr Brad Stanfield's Sleep by Dr Brad contains 2,400 mg of glycine alongside low-dose, sustained-release melatonin (0.8 mg) and magnesium bisglycinate (126 mg elemental) — three ingredients targeting different sleep mechanisms: glycine for core body temperature reduction, melatonin for circadian signaling, and magnesium for relaxation and reduced sleep latency. The glycine dose is close to the 3 g studied in clinical trials, and the 2,400 mg counts the glycine carried by the magnesium bisglycinate chelate.

5. Safety and Side Effects

General Tolerability

In trials, glycine has generally been well tolerated, including at high doses ^{[21, 22]}. In a schizophrenia trial that added 0.8 g/kg body weight of glycine a day for 6 weeks, glycine was well tolerated ^[22].

Reported Side Effects

Side effects appear to be uncommon at supplement doses; the bladder study of 3 g twice a day reported no adverse events ^[18]. Possible side effects include:

• Gastrointestinal effects: Stomach upset, nausea or diarrhoea may occur, and are more likely at high doses
• Nausea at very high doses: In an OCD trial of glycine titrated to 60 g a day, many participants stopped, mainly because of the taste or nausea ^[29]
• Drowsiness: Occasionally noted at higher doses, consistent with glycine's mechanism of action on sleep
• Migraine: Studies have found higher glycine levels in the platelets of people with migraine with aura ^[37] and in the saliva of people with migraine ^[38]. This does not show that glycine supplements cause migraine.

Glycine Does NOT Cause Morning Grogginess

Unlike high-dose melatonin supplements, glycine does not cause next-morning grogginess. Clinical studies consistently report that glycine improves next-day alertness and reduces daytime fatigue rather than causing sedation ^{[15, 16, 17]}. This may be because glycine appears to promote sleep through thermoregulatory mechanisms (core body temperature reduction, shown in rats) rather than through pharmacological sedation ^{[13, 14]}.

FDA Classification Note

The FDA no longer regards glycine as generally recognized as safe (GRAS) for use in human food, because high levels caused adverse effects in experimental animals ^[39]. Food makers may add it only for specific technical uses, such as hiding saccharin's bitter aftertaste in drinks, at most 0.2% of the finished beverage ^[12]. These food rules do not cover dietary supplements, where glycine is sold legally.

Special Populations

• Pregnancy and breastfeeding: If you are pregnant or breastfeeding, check with your doctor before you take glycine.
• Children: Safety data in pediatric populations are insufficient. Glycine supplements are not recommended for children.
• Non-ketotic hyperglycinaemia (NKH): In this rare inherited disorder, large amounts of glycine build up in all body tissues, including the brain, and treatment aims to lower plasma glycine ^[43]. Supplements add glycine, so anyone with NKH should check with their specialist before taking one.
• Epilepsy: If you have epilepsy, check with your doctor before taking glycine.

Laxative Effect Comparison

Glycine may occasionally cause diarrhoea; if it does, lower the dose or stop.

6. Drug Interactions

Some medicines may interact with glycine. Known and theoretical interactions include:

Key Interaction Details

Clozapine: The interaction between glycine and clozapine is the most clinically significant. Potkin et al. (1999) found that high-dose glycine appeared to interfere with clozapine's efficacy in treating schizophrenia ^[23]. While glycine enhances NMDA receptor function (which may benefit negative symptoms), clozapine already has glycine-site NMDA receptor activity, and the combination may paradoxically reduce therapeutic benefit. This combination should be avoided.

Blood pressure medications: Blood pressure fell while people took glycine in one small study ^[18]. If you take blood pressure medicine, check with your doctor before you take glycine, in case your blood pressure drops too far.

7. Dietary Sources

Gelatin, skin and other protein-rich foods hold the most glycine per 100 g ^[41].

Top Food Sources

Source: USDA FoodData Central, SR Legacy data ^[41]. The per-serving figures multiply the value per 100 g by the serving weight USDA lists.

Dietary Context

Gelatin and skin hold more glycine per 100 g than lean meat, fish, eggs or lentils ^[41].