NAC, Cysteine, Glycine and Other Glutathione Precursors: Where Each Is Covered
Glutathione is built from amino acids. This guide explains what a precursor is, what two GlyNAC trials in older adults found, and where NAC, glycine and cysteine are covered.
Content last updated . This page has not been medically reviewed.
The question this page answers
If the body makes glutathione from simpler building blocks, can taking those building blocks raise it? This page explains the idea and points to the pages that cover each ingredient. It does not recommend any supplement.How the sources describe the building blocks
MedlinePlus Genetics describes glutathione as a small molecule made of three amino acids, put together by a chain of reactions in most of the body's cells. [1] A 2013 review says the supply of the sulfur-containing amino acid cysteine is a key factor in how fast the body makes glutathione. [2] A 2022 trial paper describes glycine and cysteine as non-essential amino acids required to generate glutathione. [3] NAC (N-acetylcysteine) is a form of cysteine that the studies below used as a supplement.Where each ingredient is covered
| Ingredient | Where to read about it |
|---|---|
| N-acetylcysteine (NAC) | More about N-acetylcysteine (NAC) → |
| NAC compared with glutathione | More about NAC compared with glutathione → |
| Glycine | More about Glycine → |
| Cysteine and protein in food | Amino Acids & Protein and Whey Protein |
| Glutathione supplements themselves | More about Glutathione supplements themselves → |
| GlyNAC in aging research | More about GlyNAC in aging research → |
What two trials of glycine plus NAC (GlyNAC) found
Frequently asked questions
What are glutathione precursors?
They are the building blocks the body uses to make glutathione, mainly the amino acids cysteine and glycine. [3][1]
Does taking NAC raise glutathione?
We do not make that claim here. The trials we read tested NAC combined with glycine, and results were mixed. See the NAC page for more. [3][4]
Is GlyNAC proven?
No. One 2022 trial in healthy older adults did not raise its main glutathione measure; a smaller 2023 trial reported improvements. [3][4]
Which amino acid limits glutathione production?
A 2013 review says cysteine availability is a key determinant. [2]
Can I take amino acids with my medicines?
Ask a pharmacist first. See Medication Interactions.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: mixed, promising but limited, and Proper evidence not found.
| Trial | Who and how long | What was found | Label |
|---|---|---|---|
| Lizzo 2022, Front Aging | 114 healthy volunteers, average age 65; GlyNAC at three amounts for 2 weeks | Well tolerated, but it did not increase the main measure of glutathione status. [3] | Mixed |
| Kumar 2023, J Gerontol | 24 older adults (12 got GlyNAC, 12 placebo) for 16 weeks, plus 12 young adults for 2 weeks | The authors report improved glutathione, oxidative stress and other measures, and call it safe and well tolerated. [4] | Promising but limited (small) |
These trials measured blood markers in specific groups. They do not show that GlyNAC prevents or treats any disease, and a change in a marker is not a health outcome. Results from GlyNAC cannot be applied to NAC alone, glycine alone, or glutathione capsules.
Safety and who should ask first
References
- National Library of Medicine. GSS gene. MedlinePlus Genetics. Read 2026-10-23.
- Lu SC. Glutathione synthesis. Biochim Biophys Acta, 2013 (PubMed abstract). Read 2026-10-23.
- Lizzo G, Migliavacca E, Lamers D, et al. A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage. Front Aging, 2022 (PubMed abstract). Read 2026-10-23.
- Kumar P, Liu C, Suliburk J, et al. Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial. J Gerontol A Biol Sci Med Sci, 2023 (PubMed abstract). Read 2026-10-23.