Type your body weight. You see the glycine and NAC the human GlyNAC trials gave for that weight — they dosed by the kilo — and, if you add what your own label gives you a day, where yours sits against them. Every trial came from one research group, and only one had a placebo; that is said beside every answer.
For 80 kg, the trials gave about
8 g glycine + 8 g NAC a day what the 2023 placebo-controlled trial gave for 80 kg — 100 mg of each per kg
The 2023 placebo-controlled trial: 8 g of glycine and 8 g of NAC a day for 80 kg (“100 mg/kg/d each of glycine and NAC”).
The earlier open trials (2011–2021): 8 g of glycine and 10.6 g of NAC a day (“glycine 1.33 mmol/kg/day and cysteine 0.81 mmol/kg/day, as NAC” — 99.8 and 132.2 mg per kg by molar mass, so about a third more NAC than the 2023 wording).
This is what the trials gave, not a dose for you: no official body sets a dose or an upper limit for glycine or NAC as a supplement, and the longer trials gave it as pharmacist-made capsules to adults whose kidney and liver tests were watched.
All 6 human GlyNAC trials we could find come from one research group (Rajagopal Sekhar’s, at Baylor College of Medicine). One had a placebo — 12 older adults on GlyNAC for 16 weeks against 12 on an alanine placebo; the other 5 were open-label, with 8 to 12 people given it for 2 to 24 weeks.
The group’s 2014 paper discloses: “R.V.S. is an inventor on U.S. patent US20110077303 with rights held by Baylor College of Medicine.” The 2023 trial’s reads: “Conflict of Interest None declared.”
| Trial | Who, how many | How long | In its own words |
|---|---|---|---|
| Kumar 2023 · placebo | 12 older adults (61–80, BMI over 27); 12 on an alanine placebo | 16 weeks | “GlyNAC supplementation in OA for 16-weeks was safe and well-tolerated.” |
| Kumar 2021 · open | 8 older adults (71–80); 8 young adults studied once, not given it | 24 weeks | “However, benefits declined after stopping GlyNAC supplementation for 12 weeks.” |
| Kumar 2020 · open | 8 people with HIV; 8 matched people without HIV, not given it | 12 weeks | “The p -values were not adjusted for multiple hypothesis testing due to the small sample size of this pilot study.” |
| Nguyen 2014 · open | 8 older men with HIV; none — before and after | 2 weeks | “These data suggest that GSH adequacy promotes metabolic health in older HIV-infected patients.” |
| Sekhar 2011 · open | 8 older adults (60–75); 8 younger adults studied once, not given it | 2 weeks | “Dietary supplementation with the glutathione precursors cysteine and glycine fully restores glutathione synthesis and concentrations and lowers levels of oxidative stress and oxidant damages.” |
| Sekhar 2011 · open | 12 adults with uncontrolled type 2 diabetes; 12 adults without diabetes studied once | 2 weeks | “A longer duration of intervention may be required to normalize synthesis and intracellular concentrations of GSH.” |
NAC is also a medicine. The FDA’s 2022 guidance: “NAC (i.e., acetylcysteine) was approved as a new drug under section 505 of the FD&C Act on September 14, 1963”, and it states “our intent to exercise enforcement discretion with respect to the sale and distribution of certain products that contain N-acetyl-L-cysteine (NAC) and are labeled as dietary supplements.” “While FDA’s full safety review of NAC remains ongoing, our initial review has not revealed safety concerns with respect to the use of this ingredient in or as a dietary supplement.”
This is not medical advice. It shows what the trials gave, not what you should take. Talk to your doctor or pharmacist before taking NAC or glycine — especially with blood thinners, antidepressants or blood-pressure medication, or are pregnant or breastfeeding; the 2023 trial asked its participants to avoid acetaminophen and alcohol.
One research group ran all six human GlyNAC trials, and they dosed by body weight. The 2023 placebo-controlled trial gave 100 mg of glycine and 100 mg of NAC per kg a day — 8 g of each for an 80 kg adult. The earlier open trials gave 1.33 mmol/kg glycine and 0.81 mmol/kg cysteine as NAC: about 8 g and 10.6 g.
How to use it
Type your body weight in kg or lb. You see the glycine and the NAC (N-acetyl-L-cysteine) that the trials gave for that weight, both ways the papers write the dose. If you take a product already, add the glycine and the NAC it gives you a day, in mg, from the Supplement Facts panel: you see each as a share of what the trials gave. It does not tell you what to take — there is no official dose for either — and it never moves your number toward the trials’.
What the trials gave, in their own words
The 2023 trial: “These supplements are filled into capsules by a pharmacist, and provided monthly to study participants at doses of 100 mg/kg/d each of glycine and NAC, and 200 mg/kg/d of alanine.” The alanine was the placebo. The group’s 2022 paper writes it the same way: “Glycine and NAC capsules were prepared by a pharmacist and dosed to provide 100 mg/kg/day of glycine, and 100 mg/kg/day of NAC.” The earlier papers write it in millimoles — the 2021 pilot: “OAs were provided capsules of glycine (1.33 mmol/kg/day) and cysteine (0.81 mmol/kg/day, provided as N-acetylcysteine [NAC]) prepared by a licensed pharmacist, and replenished every 4-weeks for 24-weeks.”
Millimoles to milligrams is our arithmetic, with PubChem’s molecular weights (glycine 75.07 g/mol, N-acetyl-L-cysteine 163.20 g/mol): 1.33 × 75.07 = 99.8 mg of glycine per kg, and 0.81 × 163.20 = 132.2 mg of NAC per kg. So the glycine is the same either way, but the earlier trials gave about a third more NAC per kg than the 2023 wording. The calculator shows both.
| Body weight | 2023 trial: glycine | 2023 trial: NAC | Earlier trials: glycine | Earlier trials: NAC |
|---|---|---|---|---|
| 50 kg (110 lb) | 5 g | 5 g | 5 g | 6.6 g |
| 60 kg (132 lb) | 6 g | 6 g | 6 g | 7.9 g |
| 70 kg (154 lb) | 7 g | 7 g | 7 g | 9.3 g |
| 80 kg (176 lb) | 8 g | 8 g | 8 g | 10.6 g |
| 90 kg (198 lb) | 9 g | 9 g | 9 g | 11.9 g |
| 100 kg (220 lb) | 10 g | 10 g | 10 g | 13.2 g |
Who ran the trials, and how big they were
Every human GlyNAC trial we could find comes from one research group: Rajagopal Sekhar’s, at Baylor College of Medicine in Houston. Six trials; only one had a placebo: the 2023 trial — “OA was randomized to receive either GlyNAC (N = 12) or isonitrogenous alanine placebo (N = 12) for 16-weeks; YA (N = 12) received GlyNAC for 2-weeks.” Its older adults were healthier than most: “OA: 61–80 years with body mass index (BMI) > 27; and YA 21–40 years.” “This RCT studied healthier OA to focus primarily on the pure effect of aging unaffected by the additional confounding disease.” The other five were open-label: 8 to 12 people, measured before and after, for 2 to 24 weeks.
The group’s 2014 paper discloses: “R.V.S. is an inventor on U.S. patent US20110077303 with rights held by Baylor College of Medicine.” The 2023 trial’s disclosure reads: “Conflict of Interest None declared.” We name both; the reader can weigh them.
What they found
The trials measured glutathione (the antioxidant glycine and cysteine are used to build), markers of oxidative stress and inflammation, insulin resistance, and in the longer trials strength, walking speed and memory tests. In the placebo-controlled trial, the GlyNAC group’s numbers moved and the placebo group’s did not — for example: “Only GlyNAC supplementation increased gait speed in OAG-16w to levels not different from YA-0w, increased upper and lower extremity muscle strength, with a trend toward increasing 6-minute walk distance (Table 2; Supplementary Figure S1).” Some measures did not move: “No changes occurred in fasting glucose concentrations or glucose tolerance tests.” “Presupplementation HRQoL was similar in OAG and OAP groups, and unaffected by GlyNAC or placebo.” And the trial’s “aging hallmarks” were not its planned outcomes: “Because the aging hallmarks were first reported after our RCT had started, they were added as exploratory outcomes after trial completion.” Its authors ask for more: “Because the trial results show that GlyNAC supplementation improves multiple age-associated abnormalities, future GlyNAC trials with larger numbers of more typical OA are warranted.”
The 2021 pilot stopped the capsules after 24 weeks: “However, benefits declined after stopping GlyNAC supplementation for 12 weeks.”
Safety, as the trials and the FDA put it
The 2023 trial: “GlyNAC supplementation in OA for 16-weeks was safe and well-tolerated.” It watched kidney and liver blood tests throughout: “Plasma creatinine, alanine, and aspartate transaminases monitored at 2-, 4-, 8-, 12-, and 16-weeks (Figure 1B) did not show any increase compared to baseline values (Table 4).” And: “Participants were asked to avoid acetaminophen and alcohol for the duration of the trial.” Twelve people for sixteen weeks is not a long-term safety record.
NAC is also a medicine. The FDA’s August 2022 guidance: “FDA has determined that NAC is excluded from the dietary supplement definition under section 201(ff)(3)(B)(i) of the FD&C Act because NAC was approved as a new drug before it was marketed as a dietary supplement or as a food.” “NAC (i.e., acetylcysteine) was approved as a new drug under section 505 of the FD&C Act on September 14, 1963”. “The purpose of this guidance is to advise dietary supplement manufacturers, distributors, and other stakeholders of our intent to exercise enforcement discretion with respect to the sale and distribution of certain products that contain N-acetyl-L-cysteine (NAC) and are labeled as dietary supplements.” “While FDA’s full safety review of NAC remains ongoing, our initial review has not revealed safety concerns with respect to the use of this ingredient in or as a dietary supplement.”
Worked examples
- 80 kg (the page’s example): the 2023 trial gave 8 g of glycine + 8 g of NAC a day; the earlier trials 8 g + 10.6 g.
- 176 lb, taking 1,200 mg glycine and 600 mg NAC a day: 176 lb is 79.8 kg. The glycine is 15% of the 8 g the trials gave; the NAC is 8% of the 2023 trial’s 8 g and 6% of the earlier trials’ 10.6 g.
- 70 kg, taking 12,000 mg of NAC a day: 171% of the 2023 trial’s 7 g and 130% of the earlier trials’ 9.3 g — more than any GlyNAC trial gave, and the page says so.
Common mistakes
- Reading a “GlyNAC” label as the trial dose. A product’s serving is whatever its label says; the trials gave about a gram of each per ten kilos of body weight, every day.
- Treating six trials from one group as six confirmations. One lab, one placebo-controlled trial of 24 older adults, healthier than most; we found no human GlyNAC trial from any other group.
- Assuming the effects last. The 2021 pilot reports benefits declined within 12 weeks of stopping.
- Mixing up the two dose wordings. 100 mg/kg of NAC and 0.81 mmol/kg of cysteine as NAC are not the same amount; the second is about 132 mg/kg.
Frequently asked questions
What is GlyNAC?
Glycine and N-acetylcysteine taken together — the name Rajagopal Sekhar’s group at Baylor College of Medicine gave the combination in its trials. Cysteine and glycine are two of the three amino acids the body builds glutathione from; NAC supplies the cysteine.
What is the GlyNAC dosage in the studies?
By body weight: the 2023 placebo-controlled trial gave “100 mg/kg/d each of glycine and NAC”; the earlier open trials gave glycine 1.33 mmol/kg/day and cysteine 0.81 mmol/kg/day as NAC — about 100 mg/kg of glycine and 132 mg/kg of NAC. For an 80 kg adult that is 8 g of each, or 8 g and 10.6 g. There is no official dose.
How much glycine and NAC did the GlyNAC trial give a 70 kg person?
7 g of glycine and 7 g of NAC a day in the 2023 trial’s wording; 7 g of glycine and 9.3 g of NAC by the earlier trials’ millimoles.
Was GlyNAC tested against a placebo?
Once: the 2023 trial gave 12 older adults GlyNAC and 12 an alanine placebo for 16 weeks. The other five human trials were open-label, with 8 to 12 people and no placebo.
Who did the GlyNAC research?
All six human trials come from Rajagopal Sekhar’s group at Baylor College of Medicine. Its 2014 paper discloses that Sekhar is an inventor on a U.S. patent whose rights are held by Baylor College of Medicine.
Is NAC a supplement or a drug?
The FDA says NAC “was approved as a new drug under section 505 of the FD&C Act on September 14, 1963”, which excludes it from the dietary supplement definition; its 2022 guidance states its “intent to exercise enforcement discretion” for products labeled as dietary supplements.
What happens when you stop GlyNAC?
In the 2021 pilot: “However, benefits declined after stopping GlyNAC supplementation for 12 weeks.”
Related tools: Glycine for Sleep (the 3 g sleep trials), the Nootropic Dose Checker and the Cost per Serving Calculator.
Read next
- 14 proven herbs, nootropics and supplements for rumination — NAC is first on the list
- Nootropics for mitochondria: which work?
- BrainMD Brain and Body Power Max review
This is not medical advice, and nothing here diagnoses, treats or prevents anything. It shows what the GlyNAC trials gave and what they reported, not what you should take; no official body sets a dose or an upper limit for glycine or NAC as a supplement. Talk to your doctor or pharmacist first — especially with blood thinners, antidepressants or blood-pressure medication, or if you are pregnant or breastfeeding. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.