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Milk Thistle (PDQ®)

Health Professional Version
Last Modified: 12/23/2013

Laboratory/Animal/Preclinical Studies

Research studies conducted in the laboratory have investigated the properties of silymarin or its isomer silybin using cell lines and animal models. Other substances in milk thistle have not been extensively studied.

Several research studies have investigated the effects of silymarin or silybin in a noncancer context. These studies have tested silymarin or silybin:

Silymarin or silybin has also been investigated in cancer models. The effects of silymarin and/or silybin have been investigated in prostate (DU 145, LNCaP, PC-3),[1-6] breast (MDA-MB 468, MCF-7),[7-9] hepatic (HepG2),[10,11] epidermoid (A431),[11] colon (Caco-2),[12] ovarian (OVCA 433, A2780),[13] histiocytic lymphoma (U-937),[14] and leukemia (HL-60) [15,16] cells. In animal tumor models, tongue cancer,[17] skin cancer,[18-23] bladder cancer,[24] and adenocarcinoma of the colon [25,26] and small intestine [26] have been investigated. These studies have tested the ability of silymarin or silibinin to:

  • Mitigate the toxicity associated with chemotherapy agents.
  • Enhance the efficacy of chemotherapy agents.
  • Inhibit the growth of cancer cell lines and inhibit tumor initiation or tumor promotion.

Although many of these studies have produced encouraging results, none of the findings have been replicated in human clinical trials.

Laboratory data suggest that silymarin and silybin protect the liver from damage induced by toxic chemicals. Animal studies have found that liver cells treated with silybin and then exposed to toxins do not incur cell damage or death at the same rate as liver cells that are not treated with silybin. This finding suggests that silybin can prevent toxins from entering the cell or effectively exports toxins out of the cell before damage ensues.[11,27-31] Alternatively, this may be related to the effect of silymarin on detoxification systems. In vitro data have shown silybin to stimulate and/or inhibit phase I detoxification pathways in silybin-treated human liver cells. However, this effect was found to be dose-dependent, and these levels are not physiologically attainable with the current manufacturer dose recommendations.[32,33]

Silymarin has been shown to stimulate phase II detoxification pathways in mice. Administration of silymarin (100 or 200 mg /kg body weight/day) to SENCAR mice for 3 days significantly increased glutathione S-transferase activity in the liver (P < .01–.001), lung (P < .05–.01), stomach (P < .05), small bowel (P < .01), and skin (P < .01). This effect appeared to be dose-dependent.[34] Administration of silymarin to rats challenged with a toxin (50 mg/kg body weight) resulted in higher levels of glutathione in liver cells, decreased levels of oxidative stress (measured by malondialdehyde concentrations), and less elevated liver function tests (measured by levels of aspartate aminotransferase [AST] and alanine aminotransferase [ALT]).[31] Silymarin and silybin have also been found to accelerate cell regeneration in the liver through stimulation of precursors to DNA synthesis and enhancement of production of the cellular enzymes required for synthesis of DNA.[35-40] Laboratory studies have also shown silymarin and silybin to be potent antioxidants.[28,29,41-48] Silymarin has been shown to mitigate oxidative stress in cells treated with pro-oxidant compounds.

A number of laboratory studies have investigated the effect of silymarin or silybin on the efficacy and toxicity of chemotherapy agents or have measured their direct cytotoxic activity. In an investigation of the effect of a variety of flavonoids on the formation of DNA damage, silymarin did not induce DNA damage in colon (Caco-2) cells, hepatoma (HepG2) cells, and human lymphocytes.[12] At higher concentrations of silymarin (400–1,000 μmol/L) DNA damage was induced in an epithelial cell line (HeLa cells). At higher concentrations (1,000 μmol/L) DNA damage was observed in human lymphocytes. Cell growth was inhibited as the flavonoid concentration was increased in human lymphocytes and HeLa cells. Only at very high concentrations was cell viability affected by silymarin in HepG2 cells. Although this study demonstrated that the flavonolignans of Silybum marianum (L.) are capable of inhibiting cellular proliferation and inducing DNA strand breaks, the results were obtained at very high concentrations that may be difficult to achieve in humans. This study also showed that silymarin does not stimulate cell growth in the HeLa, Burkitt lymphoma, and human hepatoma cell lines.

Silymarin has also been investigated as a possible adjunctive agent in mitigating some of the toxicity associated with chemotherapy agents. Silybin and silychristin exerted a protective effect on monkey kidney cells exposed to vincristine and especially cisplatin chemotherapy.[49] Silybin (200 mg/kg body weight) administration with cisplatin in rats resulted in statistically significant reductions in measures of kidney toxicity.[50] Significant decreases in weight loss, faster recovery of urinary osmolality measures, and depressions in the increase in activity of urinary alanine aminopeptidase ([AAP], a marker of kidney toxicity) were observed. Silybin had no effect on magnesium excretion or glomerular function. Silybin (2 g /kg body weight) administration in rats receiving cisplatin prevented reductions in creatinine clearance, increases in urea plasma levels, and large increases in urinary AAP.[51] No effect on magnesium excretion was observed. Silybin did not interfere with the antineoplastic effects of cisplatin or ifosfamide in germ cell tumors. In experiments with ovarian and breast cancer cell lines, silybin potentiated the effect of cisplatin and doxorubicin.[13] IdB 1,016, a form of silybin bound to a phospholipid complex, was found to enhance the activity of cisplatin against A2780 ovarian cancer cells but had no effect on its own.[52] Silybin increased the chemosensitivity of DU 145 prostate cancer cells resistant to chemotherapy.[53]

Studies have also investigated the effect of silymarin on tumor initiation and promotion. Silymarin appears to have a chemopreventive effect through perturbations in the cell cycle, altering cell signaling that induces cellular proliferation, affecting angiogenesis, or through its anti-inflammatory properties.[1,7,13,19,54] These findings have been supported in human prostate, breast, ectocervical, ovarian, hepatic, leukemia, and epidermoid cell lines.[4,7,9,10,15,55] An investigation of the effect of silymarin on ultraviolet B radiation-induced nonmelanoma skin cancer in mice found that silymarin treatment significantly reduced tumor incidence (P < .003), tumor multiplicity (P < .0001), and tumor volume (P < .0001).[19] These findings suggest that silymarin plays a prominent role in the reduction of cancer cells and in preventing the formation of cancer cells. A number of studies have investigated the mechanism through, which silymarin may affect tumor promotion in mouse skin tumor models. Studies have found that silymarin reduces transcription of markers of tumor promotion and activity,[19] inhibits transcription of tumor promoters,[56] stimulates antioxidant activities,[19,23] interferes with cell signaling,[55] inhibits inflammatory actions,[19,22] and modulates cell-cycle regulation.[57]

In prostate cancer cell lines, silybin has been shown to inhibit growth factors and stimulate cell growth,[1-3,5] promote cell cycle arrest,[1,4] and inhibit antiapoptotic activity.[53] In rats with azoxymethane -induced colon cancer, dietary silymarin resulted in a reduction in the incidence and multiplicity of adenocarcinoma of the colon in a dose-dependent manner.[25,26] Dietary silymarin had no effect on small intestinal adenocarcinoma,[26] but exerted a preventive effect in mice with N-butyl-N-(4-hydroxybutyl) nitrosamine –induced bladder cancer [24] and in F344 rats with 4-nitroquinoline 1-oxide –induced cancer of the tongue.[17] Dietary silybin administered to nude mice with prostate carcinoma increased production of insulin-like growth factor-binding protein-3 in the plasma of mice and significantly inhibited tumor volume (P < .05).[2] Silibinin administered twice daily reduced the growth of colorectal tumor xenografts in mice for a period of 6 weeks.[58,59]

  1. Zi X, Agarwal R: Silibinin decreases prostate-specific antigen with cell growth inhibition via G1 arrest, leading to differentiation of prostate carcinoma cells: implications for prostate cancer intervention. Proc Natl Acad Sci U S A 96 (13): 7490-5, 1999.  [PUBMED Abstract]

  2. Singh RP, Dhanalakshmi S, Tyagi AK, et al.: Dietary feeding of silibinin inhibits advance human prostate carcinoma growth in athymic nude mice and increases plasma insulin-like growth factor-binding protein-3 levels. Cancer Res 62 (11): 3063-9, 2002.  [PUBMED Abstract]

  3. Zi X, Zhang J, Agarwal R, et al.: Silibinin up-regulates insulin-like growth factor-binding protein 3 expression and inhibits proliferation of androgen-independent prostate cancer cells. Cancer Res 60 (20): 5617-20, 2000.  [PUBMED Abstract]

  4. Zi X, Grasso AW, Kung HJ, et al.: A flavonoid antioxidant, silymarin, inhibits activation of erbB1 signaling and induces cyclin-dependent kinase inhibitors, G1 arrest, and anticarcinogenic effects in human prostate carcinoma DU145 cells. Cancer Res 58 (9): 1920-9, 1998.  [PUBMED Abstract]

  5. Sharma Y, Agarwal C, Singh AK, et al.: Inhibitory effect of silibinin on ligand binding to erbB1 and associated mitogenic signaling, growth, and DNA synthesis in advanced human prostate carcinoma cells. Mol Carcinog 30 (4): 224-36, 2001.  [PUBMED Abstract]

  6. Flaig TW, Glodé M, Gustafson D, et al.: A study of high-dose oral silybin-phytosome followed by prostatectomy in patients with localized prostate cancer. Prostate 70 (8): 848-55, 2010.  [PUBMED Abstract]

  7. Bhatia N, Zhao J, Wolf DM, et al.: Inhibition of human carcinoma cell growth and DNA synthesis by silibinin, an active constituent of milk thistle: comparison with silymarin. Cancer Lett 147 (1-2): 77-84, 1999.  [PUBMED Abstract]

  8. Jiang C, Agarwal R, Lü J: Anti-angiogenic potential of a cancer chemopreventive flavonoid antioxidant, silymarin: inhibition of key attributes of vascular endothelial cells and angiogenic cytokine secretion by cancer epithelial cells. Biochem Biophys Res Commun 276 (1): 371-8, 2000.  [PUBMED Abstract]

  9. Zi X, Feyes DK, Agarwal R: Anticarcinogenic effect of a flavonoid antioxidant, silymarin, in human breast cancer cells MDA-MB 468: induction of G1 arrest through an increase in Cip1/p21 concomitant with a decrease in kinase activity of cyclin-dependent kinases and associated cyclins. Clin Cancer Res 4 (4): 1055-64, 1998.  [PUBMED Abstract]

  10. Saliou C, Rihn B, Cillard J, et al.: Selective inhibition of NF-kappaB activation by the flavonoid hepatoprotector silymarin in HepG2. Evidence for different activating pathways. FEBS Lett 440 (1-2): 8-12, 1998.  [PUBMED Abstract]

  11. Shear NH, Malkiewicz IM, Klein D, et al.: Acetaminophen-induced toxicity to human epidermoid cell line A431 and hepatoblastoma cell line Hep G2, in vitro, is diminished by silymarin. Skin Pharmacol 8 (6): 279-91, 1995.  [PUBMED Abstract]

  12. Duthie SJ, Johnson W, Dobson VL: The effect of dietary flavonoids on DNA damage (strand breaks and oxidised pyrimdines) and growth in human cells. Mutat Res 390 (1-2): 141-51, 1997.  [PUBMED Abstract]

  13. Scambia G, De Vincenzo R, Ranelletti FO, et al.: Antiproliferative effect of silybin on gynaecological malignancies: synergism with cisplatin and doxorubicin. Eur J Cancer 32A (5): 877-82, 1996.  [PUBMED Abstract]

  14. Manna SK, Mukhopadhyay A, Van NT, et al.: Silymarin suppresses TNF-induced activation of NF-kappa B, c-Jun N-terminal kinase, and apoptosis. J Immunol 163 (12): 6800-9, 1999.  [PUBMED Abstract]

  15. Kang SN, Lee MH, Kim KM, et al.: Induction of human promyelocytic leukemia HL-60 cell differentiation into monocytes by silibinin: involvement of protein kinase C. Biochem Pharmacol 61 (12): 1487-95, 2001.  [PUBMED Abstract]

  16. Clinton SK: The dietary antioxidant network and prostate carcinoma. Cancer 86 (9): 1629-31, 1999.  [PUBMED Abstract]

  17. Yanaida Y, Kohno H, Yoshida K, et al.: Dietary silymarin suppresses 4-nitroquinoline 1-oxide-induced tongue carcinogenesis in male F344 rats. Carcinogenesis 23 (5): 787-94, 2002.  [PUBMED Abstract]

  18. Agarwal R, Katiyar SK, Lundgren DW, et al.: Inhibitory effect of silymarin, an anti-hepatotoxic flavonoid, on 12-O-tetradecanoylphorbol-13-acetate-induced epidermal ornithine decarboxylase activity and mRNA in SENCAR mice. Carcinogenesis 15 (6): 1099-103, 1994.  [PUBMED Abstract]

  19. Katiyar SK, Korman NJ, Mukhtar H, et al.: Protective effects of silymarin against photocarcinogenesis in a mouse skin model. J Natl Cancer Inst 89 (8): 556-66, 1997.  [PUBMED Abstract]

  20. Lahiri-Chatterjee M, Katiyar SK, Mohan RR, et al.: A flavonoid antioxidant, silymarin, affords exceptionally high protection against tumor promotion in the SENCAR mouse skin tumorigenesis model. Cancer Res 59 (3): 622-32, 1999.  [PUBMED Abstract]

  21. Singh RP, Tyagi AK, Zhao J, et al.: Silymarin inhibits growth and causes regression of established skin tumors in SENCAR mice via modulation of mitogen-activated protein kinases and induction of apoptosis. Carcinogenesis 23 (3): 499-510, 2002.  [PUBMED Abstract]

  22. Zhao J, Sharma Y, Agarwal R: Significant inhibition by the flavonoid antioxidant silymarin against 12-O-tetradecanoylphorbol 13-acetate-caused modulation of antioxidant and inflammatory enzymes, and cyclooxygenase 2 and interleukin-1alpha expression in SENCAR mouse epidermis: implications in the prevention of stage I tumor promotion. Mol Carcinog 26 (4): 321-33, 1999.  [PUBMED Abstract]

  23. Zhao J, Lahiri-Chatterjee M, Sharma Y, et al.: Inhibitory effect of a flavonoid antioxidant silymarin on benzoyl peroxide-induced tumor promotion, oxidative stress and inflammatory responses in SENCAR mouse skin. Carcinogenesis 21 (4): 811-6, 2000.  [PUBMED Abstract]

  24. Vinh PQ, Sugie S, Tanaka T, et al.: Chemopreventive effects of a flavonoid antioxidant silymarin on N-butyl-N-(4-hydroxybutyl)nitrosamine-induced urinary bladder carcinogenesis in male ICR mice. Jpn J Cancer Res 93 (1): 42-9, 2002.  [PUBMED Abstract]

  25. Kohno H, Tanaka T, Kawabata K, et al.: Silymarin, a naturally occurring polyphenolic antioxidant flavonoid, inhibits azoxymethane-induced colon carcinogenesis in male F344 rats. Int J Cancer 101 (5): 461-8, 2002.  [PUBMED Abstract]

  26. Gershbein LL: Action of dietary trypsin, pressed coffee oil, silymarin and iron salt on 1,2-dimethylhydrazine tumorigenesis by gavage. Anticancer Res 14 (3A): 1113-6, 1994 May-Jun.  [PUBMED Abstract]

  27. Campos R, Garrido A, Guerra R, et al.: Silybin dihemisuccinate protects against glutathione depletion and lipid peroxidation induced by acetaminophen on rat liver. Planta Med 55 (5): 417-9, 1989.  [PUBMED Abstract]

  28. Farghali H, Kameniková L, Hynie S, et al.: Silymarin effects on intracellular calcuim and cytotoxicity: a study in perfused rat hepatocytes after oxidative stress injury. Pharmacol Res 41 (2): 231-7, 2000.  [PUBMED Abstract]

  29. Lettéron P, Labbe G, Degott C, et al.: Mechanism for the protective effects of silymarin against carbon tetrachloride-induced lipid peroxidation and hepatotoxicity in mice. Evidence that silymarin acts both as an inhibitor of metabolic activation and as a chain-breaking antioxidant. Biochem Pharmacol 39 (12): 2027-34, 1990.  [PUBMED Abstract]

  30. Valenzuela A, Guerra R, Garrido A: Silybin dihemisuccinate protects rat erythrocytes against phenylhydrazine-induced lipid peroxidation and hemolysis. Planta Med 53 (5): 402-5, 1987.  [PUBMED Abstract]

  31. Campos R, Garrido A, Guerra R, et al.: Acetaminophen hepatotoxicity in rats is attenuated by silybin dihemisuccinate. Prog Clin Biol Res 280: 375-8, 1988.  [PUBMED Abstract]

  32. Zuber R, Modrianský M, Dvorák Z, et al.: Effect of silybin and its congeners on human liver microsomal cytochrome P450 activities. Phytother Res 16 (7): 632-8, 2002.  [PUBMED Abstract]

  33. Venkataramanan R, Ramachandran V, Komoroski BJ, et al.: Milk thistle, a herbal supplement, decreases the activity of CYP3A4 and uridine diphosphoglucuronosyl transferase in human hepatocyte cultures. Drug Metab Dispos 28 (11): 1270-3, 2000.  [PUBMED Abstract]

  34. Zhao J, Agarwal R: Tissue distribution of silibinin, the major active constituent of silymarin, in mice and its association with enhancement of phase II enzymes: implications in cancer chemoprevention. Carcinogenesis 20 (11): 2101-8, 1999.  [PUBMED Abstract]

  35. Sonnenbichler J, Mattersberger J, Rosen H: [Stimulation of RNA synthesis in rat liver and isolated hepatocytes by silybin, an antihepatotoxic agent from Silybum marianum L. Gaertn (author's transl)] Hoppe Seylers Z Physiol Chem 357 (8): 1171-80, 1976.  [PUBMED Abstract]

  36. Sonnenbichler J, Zetl I: [Mechanism of action of silibinin. V. Effect of silibinin on the synthesis of ribosomal RNA, mRNA and tRNA in rat liver in vivo] Hoppe Seylers Z Physiol Chem 365 (5): 555-66, 1984.  [PUBMED Abstract]

  37. Sonnenbichler J, Zetl I: Biochemical effects of the flavonolignane silibinin on RNA, protein and DNA synthesis in rat livers. Prog Clin Biol Res 213: 319-31, 1986.  [PUBMED Abstract]

  38. Sonnenbichler J, Goldberg M, Hane L, et al.: Stimulatory effect of Silibinin on the DNA synthesis in partially hepatectomized rat livers: non-response in hepatoma and other malign cell lines. Biochem Pharmacol 35 (3): 538-41, 1986.  [PUBMED Abstract]

  39. Machicao F, Sonnenbichler J: Mechanism of the stimulation of RNA synthesis in rat liver nuclei by silybin. Hoppe Seylers Z Physiol Chem 358 (2): 141-7, 1977.  [PUBMED Abstract]

  40. Dehmlow C, Erhard J, de Groot H: Inhibition of Kupffer cell functions as an explanation for the hepatoprotective properties of silibinin. Hepatology 23 (4): 749-54, 1996.  [PUBMED Abstract]

  41. Valenzuela A, Guerra R, Videla LA: Antioxidant properties of the flavonoids silybin and (+)-cyanidanol-3: comparison with butylated hydroxyanisole and butylated hydroxytoluene. Planta Med (6): 438-40, 1986.  [PUBMED Abstract]

  42. Valenzuela A, Aspillaga M, Vial S, et al.: Selectivity of silymarin on the increase of the glutathione content in different tissues of the rat. Planta Med 55 (5): 420-2, 1989.  [PUBMED Abstract]

  43. Mira ML, Azevedo MS, Manso C: The neutralization of hydroxyl radical by silibin, sorbinil and bendazac. Free Radic Res Commun 4 (2): 125-9, 1987.  [PUBMED Abstract]

  44. Mira L, Silva M, Manso CF: Scavenging of reactive oxygen species by silibinin dihemisuccinate. Biochem Pharmacol 48 (4): 753-9, 1994.  [PUBMED Abstract]

  45. Koch HP, Löffler E: Influence of silymarin and some flavonoids on lipid peroxidation in human platelets. Methods Find Exp Clin Pharmacol 7 (1): 13-8, 1985.  [PUBMED Abstract]

  46. Garrido A, Arancibia C, Campos R, et al.: Acetaminophen does not induce oxidative stress in isolated rat hepatocytes: its probable antioxidant effect is potentiated by the flavonoid silybin. Pharmacol Toxicol 69 (1): 9-12, 1991.  [PUBMED Abstract]

  47. Bosisio E, Benelli C, Pirola O: Effect of the flavanolignans of Silybum marianum L. on lipid peroxidation in rat liver microsomes and freshly isolated hepatocytes. Pharmacol Res 25 (2): 147-54, 1992 Feb-Mar.  [PUBMED Abstract]

  48. Altorjay I, Dalmi L, Sári B, et al.: The effect of silibinin (Legalon) on the the free radical scavenger mechanisms of human erythrocytes in vitro. Acta Physiol Hung 80 (1-4): 375-80, 1992.  [PUBMED Abstract]

  49. Sonnenbichler J, Scalera F, Sonnenbichler I, et al.: Stimulatory effects of silibinin and silicristin from the milk thistle Silybum marianum on kidney cells. J Pharmacol Exp Ther 290 (3): 1375-83, 1999.  [PUBMED Abstract]

  50. Gaedeke J, Fels LM, Bokemeyer C, et al.: Cisplatin nephrotoxicity and protection by silibinin. Nephrol Dial Transplant 11 (1): 55-62, 1996.  [PUBMED Abstract]

  51. Bokemeyer C, Fels LM, Dunn T, et al.: Silibinin protects against cisplatin-induced nephrotoxicity without compromising cisplatin or ifosfamide anti-tumour activity. Br J Cancer 74 (12): 2036-41, 1996.  [PUBMED Abstract]

  52. Giacomelli S, Gallo D, Apollonio P, et al.: Silybin and its bioavailable phospholipid complex (IdB 1016) potentiate in vitro and in vivo the activity of cisplatin. Life Sci 70 (12): 1447-59, 2002.  [PUBMED Abstract]

  53. Dhanalakshmi S, Singh RP, Agarwal C, et al.: Silibinin inhibits constitutive and TNFalpha-induced activation of NF-kappaB and sensitizes human prostate carcinoma DU145 cells to TNFalpha-induced apoptosis. Oncogene 21 (11): 1759-67, 2002.  [PUBMED Abstract]

  54. Zi X, Agarwal R: Modulation of mitogen-activated protein kinase activation and cell cycle regulators by the potent skin cancer preventive agent silymarin. Biochem Biophys Res Commun 263 (2): 528-36, 1999.  [PUBMED Abstract]

  55. Ahmad N, Gali H, Javed S, et al.: Skin cancer chemopreventive effects of a flavonoid antioxidant silymarin are mediated via impairment of receptor tyrosine kinase signaling and perturbation in cell cycle progression. Biochem Biophys Res Commun 247 (2): 294-301, 1998.  [PUBMED Abstract]

  56. Zi X, Mukhtar H, Agarwal R: Novel cancer chemopreventive effects of a flavonoid antioxidant silymarin: inhibition of mRNA expression of an endogenous tumor promoter TNF alpha. Biochem Biophys Res Commun 239 (1): 334-9, 1997.  [PUBMED Abstract]

  57. Singh RP, Agarwal R: Flavonoid antioxidant silymarin and skin cancer. Antioxid Redox Signal 4 (4): 655-63, 2002.  [PUBMED Abstract]

  58. Kaur M, Velmurugan B, Tyagi A, et al.: Silibinin suppresses growth and induces apoptotic death of human colorectal carcinoma LoVo cells in culture and tumor xenograft. Mol Cancer Ther 8 (8): 2366-74, 2009.  [PUBMED Abstract]

  59. Velmurugan B, Gangar SC, Kaur M, et al.: Silibinin exerts sustained growth suppressive effect against human colon carcinoma SW480 xenograft by targeting multiple signaling molecules. Pharm Res 27 (10): 2085-97, 2010.  [PUBMED Abstract]