Liver and Antioxidant Systems: What the Evidence on Milk Thistle, NAC, and Glutathione Shows

The liver carries out hundreds of metabolic and processing functions, and certain nutrients are studied in relation to it and to the body's natural antioxidant defenses. Milk thistle (silymarin), glutathione, and N-Acetyl-Cysteine each have distinct roles in the body's glutathione and antioxidant pathways; the human evidence for each, and its limits, is summarized below. FormulaForge ranks every ingredient by the bioavailability of its available forms so you can compare forms by that one measure.

Updated 2026 · Reviewed by Dr. Brennan Commerford, D.C.

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Frequently Asked Questions

What supplements may support healthy liver function?

Milk thistle (standardized for silymarin), glutathione, and N-Acetyl-Cysteine (NAC) are among the most studied ingredients in relation to the liver and the body's natural antioxidant systems. These supplements are not intended to diagnose, treat, cure, or prevent any liver disease. Consult a qualified healthcare provider for any liver-health concerns or before combining supplements with medications.

Does milk thistle support healthy liver function?

Milk thistle is standardized for silymarin, a group of plant compounds studied in relation to the liver. A systematic review with meta-analysis of trials in patients with liver disease (de Avelar et al. 2017; PMID 28785154) found silymarin produced small reductions in the liver enzymes ALT and AST that the authors judged not clinically relevant, with no significant change in γGT; the included trials were heterogeneous and of low methodological quality. Evidence in people without liver disease has not been established by this review. These are structure/function observations — milk thistle is not a treatment for any liver disease.

What is glutathione and how is it studied for liver support?

Glutathione is the body's primary intracellular antioxidant and plays a central role in the liver's natural metabolic-processing pathways. A randomized controlled trial of oral glutathione supplementation (Richie et al. 2015; PMID 24791752) reported that daily oral glutathione was associated with increased body stores of glutathione versus placebo. These are structure/function claims only.

How does N-Acetyl-Cysteine (NAC) relate to glutathione?

N-Acetyl-Cysteine is a precursor that the body can use to synthesize glutathione. A review of NAC's mechanism of action (Pedre et al. 2021; PMID 34171332) argues that this glutathione-precursor role explains NAC's effects only in specific circumstances, and that its conversion to hydrogen sulfide and sulfane sulfur species may explain many of them. These are structure/function observations — NAC is not a treatment for any condition, and it can interact with medications, so discuss it with your healthcare provider before use.