GlyNAC is simply a term used to describe co-administered glycine and n-acetylcysteine (NAC). Like NAC, GlyNAC is thought to reduce oxidative stress by increasing levels of glutathione (the most abundant intracellular antioxidant).^[1]

Preliminary research suggests that GlyNAC may reduce oxidative stress and improve metabolic health in conditions characterized by high levels of oxidative stress, such as type 2 diabetes (T2D), human immunodeficiency virus (HIV), and aging.^[2][3] As is the case with n-acetylcysteine, these benefits are largely brought about by increasing intracellular levels of the antioxidant glutathione.^[4]

Before discussing specific outcomes, it’s worth underscoring that, as of 2024, most studies on GlyNAC follow the same general methodology. People in the treatment group, who all have some condition of interest (e.g., people with HIV, people with T2D, or older people), receive some quantity of GlyNAC daily; their biomarkers of oxidative stress and metabolic health are measured at baseline, after the treatment period, and several weeks after the treatment has ceased. These biomarkers are compared to those of a group without the condition of interest (e.g., people without HIV, people without T2D, or young people) who have not received the treatment. Generally speaking, GlyNAC is able to shift the biomarkers of the treatment group to more closely resemble (and sometimes equal) those of the non-treatment group, and these biomarkers then return to baseline (i.e., worsen) after treatment is discontinued. This study design is certainly useful, especially with small groups, but the literature would still benefit from more randomized controlled trials.

With respect to specific outcomes, GlyNAC seems able to improve (i.e., reduce) fasting respiratory quotient, glucose oxidation, insulin resistance, and plasma free fatty acids in people with T2D.^[5][1]

In people with HIV, GlyNAC has been reported to improve fasting glucose levels, measures of oxidative stress like thiobarbituric acid reactive substances (TBARS) and F2-isoprostane, and scores on the physical and mental components of the SF-36, which evaluates quality of life.^[6][3]

One randomized trial in healthy older adults found that GlyNAC didn’t always raise blood levels of glutathione sulfhydryl (GSH), the reduced form of glutathione, and that GlyNAC’s ability to do so may be dependent on a person’s baseline GSH status (i.e., people with low GSH may benefit from GlyNAC, while people with normal levels of GSH may not).^[7]

No notable side effects have been reported in the GlyNAC literature, although there have been some documented instances of NAC causing nausea, vomiting, and diarrhea.^[8][9]

When NAC or GlyNAC are taken intravenously, NAC overdose is possible, and can result in red blood cell breakdown (hemolysis), low blood platelet count (thrombocytopenia), kidney failure, and possibly death.^[10]

GlycNAC is thought to provide its benefits largely by increasing the production of GSH. GlyNAC is simply glycine and cysteine (in the form of n-acetylcysteine), which are two of the three substrates necessary for the synthesis of GSH (via two enzymes: glutamate cysteine ligase and glutathione synthase).^[2]

As well as acting as substrates from which GSH can be formed, glycine and cysteine also play their own role in many biochemical reactions, and thus should be kept at proper levels. Glycine contributes methyl groups (-CH₃) to many chemical reactions (such as those involved in regulating gene expression), is a key component of cartilage, and is a neurotransmitter. Cysteine similarly donates sulfhydryl groups (-SH) to chemical reactions, binds to metal ions, and supports protein structure via the formation of disulfide bonds.^[11][12]