IngredientsGuanidinoacetic acid (GAA), also known as glycocyamine, betacyamine, or N-amidinoglycine, belongs to the class of organic compounds known as alpha amino acids and derivatives. Its systematic chemical name is N-(aminoiminomethyl)-glycine; it is the precursor to creatine, which, together with phosphocreatine, is intrinsically involved in cellular energy metabolism through adenosine triphosphate (ATP) regeneration. GAA carries the chemical formula C3H7N3O2 and is produced endogenously in the human body from the non-essential amino acids glycine and arginine in a reaction controlled by the enzyme L-arginine:glycine amidinotransferase (AGAT).
Guanidinoacetic acid (GAA, also known as glycocyamine or guanidinoacetate) is a naturally occurring alpha amino acid derivative and newly recognized dietary compound obtainable from different foods and nutritional supplements. It is the natural precursor of creatine, and it was first identified as a natural compound in humans approximately 80 years ago. More precisely, guanidinoacetic acid was isolated for the first time in 1934 by C. J. Weber from the urine of dogs and humans, who already assumed that it was a metabolic precursor of creatine.
The content of GAA varies across different foods. Meat-based products contain the highest relative amount of GAA (approximately 50 mg per kg), followed by a dairy group (approximately 0.3 mg per kg), and plant-based foods (approximately 1 µg per kg). GAA is a natural amino acid derivative involved in several metabolic pathways across the human body, including creatine biosynthesis, arginine utilization, and neuromodulation. Apart from GAA synthesized internally from glycine and arginine, total daily exposure to GAA also involves exogenous dietary sources. Specific types of meat offer even higher concentrations: pork and poultry render up to 160 mg of GAA per kilogram of food, while GAA supplements can provide up to 1000 mg per single serving.
GAA-containing foods comprise 22.6% of all foods consumed in a population survey. The most prevalent dietary sources of GAA were meat-based foods (51.6%), followed by a dairy group (42.6%), and apple (5.9%). The mean dietary intake of GAA was 9.9 ± 9.7 mg per day, with the highest consumption recorded in a 50-year-old man at 116.0 mg/day. Men consumed more GAA than women, and a significant age-associated reduction in dietary GAA intake was found.
GAA is a naturally occurring alpha amino acid derivative and newly recognized dietary compound obtainable from different foods and nutritional supplements. Anecdotal evidence suggests that GAA exposure from supplements might be a major source of GAA supply, out-competing other food sources by several orders of magnitude. Oral supplemental preparations — as characterized in the NIH dietary supplement label database — are typically presented as powders or capsules in single-ingredient or combination formulas. The co-administration of creatine and GAA has emerged as an innovative approach to potentially enhance energy metabolism. This novel blend has been suggested to offer a more effective and safe alternative in experimental and clinical nutrition. Currently, over 100 nutritional supplements containing creatine and GAA are available on the international market.
GAA (also known as glycocyamine or betacyamine) has been investigated as an energy-boosting dietary supplement in humans for more than 70 years. The history of its deliberate therapeutic application, distinct from its identity as an endogenous metabolite, dates primarily to the mid-twentieth century in clinical medicine rather than to any particular ethnobotanical tradition. GAA was not used in the context of plant-based herbal medicine; its applications emerged from biochemical pharmacology.
In the 1950s, GAA's use as a therapeutic agent was explored, showing that supplemental GAA improved patient-reported outcomes and work capacity in clinical populations. More specifically, early clinical studies revealed an improved sense of well-being, less fatigue, and enhanced work capacity after oral administration of GAA and the methyl donor betaine in patients with heart disease and disability resulting from acute anterior poliomyelitis. In these studies, betaine was supplied in a three- to fivefold molar excess in relation to GAA.
Early clinical studies from the 1950s revealed favorable effects of GAA (also known as glycocyamine) in patients with chronic illness, including heart disease, arthritis, and depression. Overall, treatment with GAA was shown to lead to an improved sense of well-being and less fatigue, yet these studies did not appear to examine changes in cellular bioenergetics after GAA administration. Furthermore, only limited information was reported about the effect of GAA on clinical markers of patients' health status.
These mid-twentieth-century investigations were conducted primarily in Europe and the United States within medical settings, not within any documented traditional indigenous or ethnopharmacological system. No WHO monograph, ESCOP monograph, or German Commission E monograph exists for GAA, consistent with its identity as an endogenous metabolite and synthetic/semi-synthetic supplement rather than a botanical.
GAA is produced endogenously in the human body from non-essential amino acids glycine and arginine in a reaction controlled by the enzyme AGAT. AGAT catalyzes the transfer of an amidino group (–C(=NH)NH2) from arginine to glycine to synthesize GAA, with ornithine as a byproduct. The reaction mainly takes place in the kidney, liver, and pancreas; however, GAA is also produced in the skeletal muscle, brain, and across the gut. In the next step, GAA is combined with S-adenosyl-L-methionine, a reaction catalyzed by guanidinoacetate N-methyltransferase (GAMT), to produce creatine and S-adenosyl-L-homocysteine.
GAA is taken up by the liver (also the pancreas and brain), where guanidinoacetate N-methyltransferase (EC 2.1.1.2) assembles the transfer of a methyl group from S-adenosylmethionine to GAA to form creatine and S-adenosylhomocysteine. Creatine is then released into the circulation, while residual GAA is excreted via the kidney.
GAA is a natural amino acid derivative that is well-recognized for its central role in the biosynthesis of creatine, an essential compound involved in cellular energy metabolism. In skeletal muscle, the guanidino group of creatine can accept a phosphate group from ATP to produce ADP and phosphocreatine. Creatinine is a spontaneously produced end product of creatine and creatine phosphate, and it is excreted in the urine.
Creatine synthesis from GAA is considered to be a major user of labile methyl groups from S-adenosylmethionine and could affect homocysteine metabolism, although studies testing the effect of creatine supplementation on plasma homocysteine concentration have shown inconsistent results.
GAA is delivered through specific membrane transporters (such as SLC6A6 and SLC6A13), previously dismissed as non-targetable carriers by other therapeutics, including creatine. This differential transporter utilization is proposed as a mechanism by which GAA may access tissues — including the brain — that are poorly supplied by direct creatine supplementation.
GAA is a natural amino acid derivative involved in several metabolic pathways across the human body, including creatine biosynthesis, arginine utilization, and neuromodulation. In preclinical research, GAA has been reported to interact with the GABAergic system. The possible toxic effects of GAA in the nervous system reported in pre-clinical research (e.g., modulation of GABA-ergic neurotransmission, impairment of brain cell development, epileptogenic activity) remain of high concern, with additional human studies required. Separately, a human study found that oral GAA loading altered plasma gamma-aminobutyric acid (GABA) levels in healthy men, suggesting a measurable neuromodulatory signal at supplemental doses (Ostojic & Stojanovic, European Journal of Nutrition, 2015).
Several bacterial species present in the human gastrointestinal system as part of normal flora, such as Corynebacterium spp., Pseudomonas aeruginosa, and Flavobacterium spp., contain the enzyme guanidinoacetase (EC 3.5.3.2). This suggests that the gut microbiome may play a role in GAA turnover, though this remains an area requiring further investigation.
GAA, the natural precursor of creatine, has potential as a dietary supplement for human nutrition; however, until recently no data were available regarding its dose-dependent pharmacokinetic (PK) behavior. A pivotal PK study enrolled 48 young adults to receive single oral doses of GAA (1.2, 2.4, and 4.8 g) or placebo and measured plasma GAA and creatine at multiple timepoints. An increase in the area under the concentration-time curve (AUC) for plasma GAA was found for the dose range tested, with 2.4- and 9.3-fold increases in AUC for every 2-fold increase in GAA dose (p < 0.0001). No differences were found for elimination half-time between the low-dose and medium-dose groups (<1.75 hours), whereas the elimination half-time was significantly longer (>2.1 hours) for the high-dose GAA regimen (p = 0.001).
After a single oral dose of 2.4 g in healthy volunteers, a substantial rise in serum GAA and creatine concentration was observed, occurring 1 hour after ingestion, with peak values of 144.9 ± 24.8 µmol/L and 65.5 ± 18.6 µmol/L, respectively.
Evidence strength: Preliminary positive; limited by small sample sizes and predominance of studies from a single research group.
The most studied application of GAA supplementation is its capacity to raise tissue creatine levels and thereby improve physical performance. Guanidinoacetic acid, a natural precursor of creatine, has been investigated as a new promising dietary supplement, yet its performance-enhancing effect, if any, has yet to be definitively established.
A key pilot RCT by Ostojic et al. (2015), published in the Journal of Investigative Medicine, enrolled 48 young participants (mean age 22.3 years) who received oral doses of GAA (1.2, 2.4, or 4.8 g/d) for 6 weeks in a randomized, double-blind, placebo-controlled design. Significant differences were observed between treatment groups for handgrip strength among participants receiving 1.2 g/d and 2.4 g/d of GAA compared with placebo (P < 0.05). In addition, muscle endurance expressed as the change from baseline in bench press repetitions was significantly greater in the 1.2 g/d group. Results from this preliminary study indicate that supplemental GAA ingested in young individuals can improve exercise performance, even at low doses (1.2 g/d).
Intervention caused a significant increase in fasting serum creatine concentrations (up to 50% after six weeks), with GAA demonstrating a low incidence of biochemical and clinical abnormalities.
Evidence strength: Preliminary; small pilot studies only.
A randomized, double-blind superiority trial published in Nutrition (2019) compared GAA with creatine versus creatine alone for tissue creatine content and exercise performance. The study found that the combination was not inferior and addressed concerns about hyperhomocysteinemia: guanidinoacetic acid with creatine compared with creatine alone for tissue creatine content, hyperhomocysteinemia, and exercise performance was evaluated in a randomized, double-blind superiority trial, published in Nutrition in 2019.
Evidence strength: Very preliminary; restricted to small pilot studies and case reports in healthy men.
A small case study published in Nutrition (2016/2017) evaluated brain creatine levels measured by magnetic resonance spectroscopy (MRS) during oral GAA administration. Five healthy men had their brain creatine levels in white matter, gray matter, cerebellum, and thalamus evaluated during 8 weeks of oral GAA administration. Volunteers were supplemented daily with 36 mg/kg body weight of GAA for the first 4 weeks; afterward the GAA dosage was titrated to ≤60 mg/kg body weight daily. At baseline, 4, and 8 weeks, the participants underwent brain MRS, clinical chemistry studies, and an open-ended questionnaire for side-effect prevalence and severity.
No participants reported any neurologic adverse event (e.g., seizures, tingling, convulsions) during the intervention. Supplemental GAA led to a region-dependent increase of the creatine pool in the human brain. This might be relevant for restoring cellular bioenergetics in disorders characterized by low brain creatine and functional enzymatic machinery for creatine synthesis, including neurodegenerative diseases, brain tumors, or cerebrovascular disease.
A secondary analysis of GAA loading trials in 19 healthy men supplemented with 3 g/d of GAA for 4 weeks and assessed by 1.5 T MRS found that an average elevation in total brain creatine content after 28-day GAA loading was 17.3% in the cerebellum (95% CI: 9.7–24.9%), 12.1% in the white matter (95% CI: 5.1–19.1%), and 8.9% in the grey matter (95% CI: 5.2–12.6%), while total creatine actually decreased in the thalamus at follow-up by 9.1% (95% CI: 6.8–11.4%).
Preliminary studies indicate that creatine supplementation (and guanidinoacetic acid; GAA) has the ability to increase brain creatine content in humans. The potential relevance to creatine transporter deficiency is theorized: because guanidinoacetic acid is capable of increasing brain creatine in normal subjects, it has been hypothesized that it may be used to increase creatine content in patients affected by creatine transporter deficiency, a rare disease in which the creatine transporter is malfunctioning, preventing creatine uptake and synthesis by the brain. This hypothesis remains largely unconfirmed in clinical trials.
Evidence strength: Preliminary; single RCT, small sample (n=21).
A randomized, double-blind crossover trial enrolled women with CFS. Twenty-one women (age 39.3 ± 8.8 years) who fulfilled the 1994 CDC criteria for CFS were randomized in a double-blind, crossover design to receive either GAA (2.4 grams per day) or placebo (cellulose) by oral administration for three months, with a two-month washout period.
After three months of intervention, participants receiving GAA significantly increased muscular creatine levels compared with the placebo group (36.3% vs. 2.4%; p < 0.01). Changes from baseline in muscular strength and aerobic power were significantly greater in the GAA group compared with placebo (p < 0.05). However, results indicated that supplemental GAA can positively affect creatine metabolism and work capacity in women with CFS, yet GAA had no effect on main clinical outcomes, such as general fatigue and musculoskeletal soreness. No effects of intervention were found for the primary efficacy outcome (MFI score for general fatigue) and musculoskeletal pain at rest and during activity.
Evidence strength: Theoretical and animal/preclinical only for disease contexts; no confirmed disease-specific human RCTs.
GAA has been investigated as an energy-boosting dietary supplement in humans for more than 70 years. GAA is suggested to effectively increase low levels of tissue creatine and improve clinical features of cardiometabolic and neurological diseases, with GAA often outcompeting traditional bioenergetics agents in maintaining ATP status during stress. These claims, however, are primarily derived from theoretical reasoning about creatine's role in those conditions, the 1950s case series, and animal data, rather than from modern controlled human clinical trials targeting specific cardiometabolic or neurological conditions.
Evidence strength: Mechanistically plausible; no published RCTs specifically using supplemental GAA as treatment; the standard-of-care model involves creatine and ornithine supplementation.
Guanidinoacetate methyltransferase (GAMT) deficiency is a rare inborn error of metabolism in which GAA accumulates to toxic levels, while creatine is not produced. Early diagnosis and treatment can lead to normal neurocognitive outcomes, prompting its recent addition to the Recommended Uniform Screening Panel. Treatment typically includes creatine and ornithine supplementation, with or without arginine restriction or sodium benzoate. In this condition, exogenous GAA supplementation is contraindicated, as it would exacerbate toxic GAA accumulation. The potential relevance of GAA for creatine transporter deficiency (a distinct condition) is under preliminary investigation as described in Section 5.3.
Evidence strength: Single pilot study; insufficient to draw conclusions.
A pilot study referenced in the literature examined guanidinoacetate-creatine supplementation in elderly subjects, with the finding that guanidinoacetate-creatine supplementation improves functional performance and muscle and brain bioenergetics in the elderly. This was published as a brief pilot report in Annals of Nutrition and Metabolism (2021) and is considered preliminary.
The following dosages are reported directly from published clinical studies and should not be interpreted as recommendations:
Progressive increases in serum and urinary concentrations of GAA and creatine were observed when increasing dosages of GAA (1.2, 2.4, and 4.8 g/d) were consumed by healthy humans for 6 weeks. The pharmacokinetic data suggest non-linear exposure at higher doses.
Preliminary human studies suggest that dietary GAA has a relatively acceptable safety profile, yet medium-term intake appears to provoke unfavorable biochemical abnormalities, such as the rise in serum homocysteine (which could be attenuated by GAA co-ingested with creatine).
The most consistently documented safety concern associated with GAA supplementation in humans is an elevation in plasma total homocysteine (T-Hcy). The enzyme guanidinoacetate N-methyltransferase catalyzes the transfer of a methyl group from S-adenosylmethionine to GAA to form creatine and S-adenosylhomocysteine. Methylation takes place mainly in the liver. Creatine is then released from the liver into the circulation where it can be taken up via a specific transporter by various tissues. Creatine synthesis from GAA is considered to be a major user of labile methyl groups from S-adenosylmethionine and could affect homocysteine metabolism.
In dose-response studies, plasma homocysteine increased by 1.4 µmol/L (15%), 2.6 µmol/L (30%), and 6.6 µmol/L (78%) when low, medium, and high levels of GAA were provided, respectively. This dose-dependent elevation in homocysteine is a clinically important finding given the association of hyperhomocysteinemia with cardiovascular risk.
An increase in serum homocysteine after GAA administration can be regarded as critical and should be prevented. A double-blind trial evaluated the effects of orally administered GAA with and without methyl group donors on serum and urine creatine concentrations and the occurrence of adverse events. Twenty volunteers were randomized to receive either GAA (2.4 g/d) or GAA with methyl donors (2.4 g/d of GAA and 1.6 g/d of betaine HCl, 5 µg/d of vitamin B12, 10 mg/d of vitamin B6, and 600 µg/d of folic acid) by oral administration for 8 weeks. Co-administration of methyl donors reduced the incidence of hyperhomocysteinemia compared with GAA administration alone.
In a post-marketing surveillance study, baseline T-Hcy levels were 11.6 ± 3.1 µmol/L. The creatine-GAA intervention induced a mild reduction in T-Hcy levels across the monitoring period (p = 0.028), with T-Hcy levels after 1, 2, 3, and 6 months being 10.4, 10.6, 10.1, and 9.3 µmol/L, respectively. These findings suggest the overall tolerability of the creatine-guanidinoacetic mixture in healthy adults, with homocysteine-increasing risk of no concern.
No serious adverse events (defined as events causing persistent or significant disability/incapacity) were reported in a six-month post-marketing surveillance study. Three adverse events (7.9%) were disclosed: one participant reported transient nausea related to the intervention, another reported gastrointestinal disturbances after taking the evening dose, and a third reported a prostate issue at the final follow-up visit, not attributed to the supplementation.
Animal studies reported neurotoxic and pro-oxidant effects of GAA accumulation, with exogenous GAA also appearing to increase methylation demand and circulating homocysteine, implying a possible metabolic burden of GAA intervention. The possible toxic effects of GAA in the nervous system reported in pre-clinical research — including modulation of GABA-ergic neurotransmission, impairment of brain cell development, and epileptogenic activity — remain of high concern, with additional human studies required before advancing GAA for human use. Notably, other adverse events demonstrated in animal studies with non-enteral administration of GAA are not confirmed in human trials with supplemental GAA thus far.
In a controlled in vitro study using hippocampal brain slices, incubation with 11.5 µM GAA (the highest concentration in the cerebrospinal fluid of GAMT-deficient patients) did not change the postsynaptic compound action potential. Even 1 or 2 mM had no effect, while 4 mM caused a reversible decrease in the potential. These concentrations far exceed those expected from dietary supplementation.
GAA is regulated primarily as an animal feed additive in jurisdictions where formal opinions have been issued. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of GAA when used as a nutritional additive in feed and water for all animal species. The FEEDAP Panel concluded that GAA at 1,200 mg/kg complete feed was safe for chickens for fattening, chickens reared for breeding/laying, piglets, and pigs for fattening. No equivalent EFSA opinion authorizing GAA as a human food or supplement ingredient has been identified. In the United States, GAA is marketed in dietary supplements, though it has not received a formal GRAS (Generally Recognized As Safe) designation for food use as of the publication of the reviewed studies.
Contraindications to creatine-GAA as described in a product's summary of product characteristics include pregnancy, lactation, and cardiovascular and kidney disease. These contraindications were operationalized as exclusion criteria in the post-marketing surveillance study and do not constitute a full regulatory label.
Whether beneficial effects outcompete side effects of GAA currently remains unknown in terms of evidence-based efficacy and safety data. The current body of human clinical research on GAA is small, primarily originates from a limited number of research groups, and most studies are short-term or pilot in nature. Long-term safety data beyond six months in humans are essentially absent. No systematic reviews or meta-analyses with pooled effect sizes specifically focused on GAA as a human dietary supplement have been published as of the time of the reviewed literature.
Health conditions that Guanidinoacetic acid may help support.
Body systems that Guanidinoacetic acid may help support.
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