September 29, 2026
N-acetylcysteine (NAC) supplies cysteine, the building block your body is shortest on when it makes glutathione.
Glutathione is the main antioxidant made inside your cells, and its levels fall with age.
Research from Baylor College of Medicine found that older adults given NAC with glycine restored glutathione and improved several markers of aging.
Key facts
- Glutathione is built from three amino acids: glutamate, cysteine and glycine. Cysteine is usually the limiting one.
- Glutathione levels decline with age, leaving cells less able to handle oxidative stress.
- GlyNAC, a combination of glycine and NAC, improved glutathione, oxidative stress, mitochondrial function and muscle strength in small trials of older adults.
- NAC has been used in medicine for decades, including as the antidote for acetaminophen overdose, so its safety profile is well known.
What is NAC?
NAC is a stable form of the amino acid cysteine. Your body converts it to cysteine, which cells then use to build glutathione. NAC has a long medical history. Hospitals use it at high doses for acetaminophen overdose, and it has been used to thin mucus in the lungs.
What is glutathione, and why does it matter for aging?
Glutathione is often called the master antioxidant. It neutralizes reactive oxygen species, recycles other antioxidants such as vitamins C and E, and helps the liver process toxins. It also protects mitochondria, which produce reactive molecules as a byproduct of making energy.
With age, glutathione levels drop. Oxidative damage accumulates in proteins, fats and DNA. That damage is linked to several hallmarks of aging, including mitochondrial dysfunction and chronic low-grade inflammation, sometimes called "inflammaging."
You can't simply swallow glutathione and expect much of it to reach your cells, because it is broken down in digestion. Supplying its building blocks is the more reliable route.
What does the research show? The GlyNAC studies
Much of the longevity interest in NAC comes from Dr. Rajagopal Sekhar's lab at Baylor College of Medicine, which studies NAC combined with glycine.
In mice. Older mice given GlyNAC showed corrected glutathione deficiency, less oxidative stress, better mitochondrial function and, in one study, longer lifespan, with a reported ~24% extension.
Pilot study in older adults. In 2021, Premranjan Kumar, Sekhar and colleagues published an open-label pilot trial in Clinical and Translational Medicine.
After 24 weeks of GlyNAC, older adults showed improvements in glutathione levels, oxidative stress, mitochondrial function, inflammation, insulin resistance, muscle strength, gait speed and some cognitive measures. Several benefits faded after supplementation stopped.
Randomized trial. A follow-up randomized, placebo-controlled trial in older adults, published in 2023 in the Journals of Gerontology, reported similar improvements over 16 weeks compared with placebo.
Two honest caveats. These trials were small, with a few dozen participants at most. And they tested NAC combined with glycine at weight-based doses higher than a typical 600 mg capsule. Ares contains NAC but not added glycine. Glycine is abundant in protein-rich foods and collagen, and some people add it separately.
How much NAC should you take?
The most common supplemental dose is 600 mg, taken once or twice a day. Ares contains 600 mg. The GlyNAC trials used higher, weight-based doses, so Ares is designed for daily maintenance rather than to replicate those protocols.
Is NAC safe?
NAC is generally well tolerated. The most common side effects are nausea, bloating and a sulfur smell. Some points to know:
- It may interact with nitroglycerin and some blood pressure medications.
- People with asthma should use it cautiously.
- Some research suggests very high doses of antioxidants could blunt certain training adaptations. Moderate doses are less of a concern.
- Pregnant or nursing women, and anyone on medication, should talk to a doctor first.
Regulatory note: The FDA has in the past questioned NAC's status as a dietary supplement because it was first approved as a drug. The agency announced enforcement discretion permitting its continued sale as a supplement.
The bottom line
NAC has a clear mechanism, a long safety record and encouraging early aging research through the GlyNAC studies. It is Ares's foundation for internal antioxidant defense. Learn how it fits with the other ingredients in My Longevity Stack, and see where it ranks in Longevity Supplements That Actually Have Human Data.
FAQ
Is it better to take NAC or glutathione? Oral glutathione is largely broken down in digestion. NAC reliably supplies cysteine, the building block your cells use to make their own glutathione.
What is GlyNAC? GlyNAC is a combination of glycine and N-acetylcysteine. It was studied at Baylor College of Medicine in older adults and improved several markers of aging in small trials.
When should I take NAC? Most people take it with a meal to reduce stomach upset. Timing matters less than taking it consistently.
Does NAC have side effects? The most common are nausea and bloating. It can interact with some medications, so check with your doctor if you take any.
Published by the SciRouter Editorial Team for general educational purposes. Last updated September 2026.
Educational disclaimer. This article is for educational and informational purposes only and is not medical advice. It summarizes published scientific research and does not endorse any specific product, supplement, drug, or treatment. These statements have not been evaluated by the Food and Drug Administration, and any products mentioned are not intended to diagnose, treat, cure, or prevent any disease. Always consult a licensed physician before starting, stopping, or changing any supplement or medication, especially if you are pregnant, nursing, have a medical condition, or take prescription medication.
