Milk Thistle vs NAC: Two Liver Supplements Compared
Milk thistle and N-acetylcysteine (NAC) are both sold for liver health. What reviews found for each, how they differ, and why neither replaces medical care.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Urgent: a suspected acetaminophen (paracetamol) overdose or any poisoning is an emergency. In the US call Poison Help 1-800-222-1222 or 911, and see poisoning: what to do first. For liver warning signs, see liver injury warning signs. Neither supplement is shown on this page to treat liver disease.
The question
Are milk thistle and NAC interchangeable "liver supplements"? No. One is a plant extract; the other is a single compound with a hospital use that differs from its use as a supplement.What each one is
- Milk thistle (Silybum marianum; the plant part is not specified in the sources we read): its main constituent is silymarin, a mixture of compounds. Historically it was used for liver disorders and to increase breast milk. That is traditional use. [1][2]
- N-acetylcysteine (NAC): a modified amino acid used as an antidote for acetaminophen overdose to prevent liver injury. [3] It is a compound, not a plant. NAC as a supplement has its own page: N-acetylcysteine.
What research found
| Question | Milk thistle | NAC |
|---|---|---|
| Alcohol-related or viral (hepatitis B or C) liver disease | A Cochrane review of 18 trials (1088 patients) rated trial quality low and questioned a benefit. [4] NCCIH: results conflicting or too limited. [1] Mixed / insufficient evidence | Proper evidence not found in the sources we read (searched PubMed for oral NAC and liver trials) |
| Fatty liver (NAFLD/NASH) | A 2024 meta-analysis of 26 trials of silymarin reported lower liver enzymes and improved liver histology, but said the effects need confirming. [5] Two NCCIH-funded trials of silymarin (hepatitis C; NASH) did not show benefit. [1] Mixed | Proper evidence not found for oral NAC in our sources |
| Acetaminophen overdose | Not a treatment | Hospital antidote. [3] This is medical care, not a supplement use. |
| Acute liver failure from other causes | Not studied in the sources we read | A 2022 meta-analysis of 7 studies (883 people) reported better survival with NAC given in hospital; an earlier review called evidence from small studies inconclusive. [6][7] Mixed; hospital setting only |
A head-to-head trial of milk thistle versus NAC: Proper evidence not found (we searched PubMed for both terms together and found no such trial).
No universal winner
The two are not rivals: the strongest NAC use is hospital treatment, and the milk thistle evidence is mixed. If you worry about your liver, a clinician can test it. See also the milk thistle profile and herbs for liver health claims checked.Frequently asked questions
Is milk thistle better than NAC for the liver?
We found no trial comparing them. Milk thistle's evidence is mixed, and the best-supported NAC use in our sources is hospital treatment. [4][3]
Does milk thistle protect the liver from alcohol?
A Cochrane review questioned a benefit in alcohol-related liver disease and noted low trial quality. [4]
Can NAC treat a Tylenol (acetaminophen) overdose at home?
No. Overdose needs emergency care: call Poison Help (1-800-222-1222) or 911. The antidote is given as medical treatment. [3]
Can milk thistle cause allergy?
Yes, especially in people allergic to related plants such as ragweed, chrysanthemum, marigold and daisy. [1]
Is milk thistle safe in pregnancy?
Little is known. Ask a clinician. [1]
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.
Safety
- Milk thistle: appears well tolerated by mouth; NIH LiverTox says it has not been implicated in liver injury. [1][8] It may cause allergic reactions in people allergic to related plants such as ragweed and daisy. [1] Little is known about pregnancy and breastfeeding. [1] Some products had silymarin amounts substantially different from the label or were contaminated. [1] See quality testing.
- NAC: LiverTox says it has not been linked to clinically apparent acute liver injury. [3] Supplement side effects, interactions and pregnancy information were not found in the sources we read for this page; see the NAC page and ask a pharmacist.
- Both: ask a clinician before using either if you have liver disease or take prescription medicines. See liver safety.
References
- National Center for Complementary and Integrative Health (NCCIH, NIH, United States). Milk Thistle: Usefulness and Safety. Available at www.nccih.nih.gov. Read 2026-10-23.
- GBIF Backbone Taxonomy, species-match service (gbif.org); accepted names checked 2026-10-23 for Ginkgo biloba L., Panax ginseng C.A.Mey., Bacopa monnieri (L.) Pennell, Hypericum perforatum L., Cinnamomum verum J.Presl, Cinnamomum aromaticum Nees, Silybum marianum (L.) Gaertn. and Camellia sinensis (L.) Kuntze.
- NIH LiverTox, Acetylcysteine entry, as indexed in PubMed. PubMed record 31643720. Read 2026-10-23.
- Cochrane Database of Systematic Reviews. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. PubMed record 17943794. Read 2026-10-23.
- Annals of Hepatology 2024. Administration of silymarin in NAFLD/NASH: a systematic review and meta-analysis. PubMed record 38579127. Read 2026-10-23.
- Annals of Gastroenterology 2022. Role of N-acetylcysteine in non-acetaminophen-related acute liver failure: an updated meta-analysis and systematic review. PubMed record 33654365. Read 2026-10-23.
- Annals of Pharmacotherapy 2004. Acetylcysteine treatment for non-acetaminophen-induced acute liver failure. PubMed record 14742832. Read 2026-10-23.
- NIH LiverTox, Milk Thistle entry, as indexed in PubMed. PubMed record 31644124. Read 2026-10-23.