Milk thistle (also known as Silybum marianum), is one of the oldest and most researched plants in the treatment of alcoholic, toxic, and viral liver diseases . It has been used for over 2000 years as a traditional herbal remedy. Its extracts are still widely used to protect the liver against toxins and to control chronic liver diseases. Milk thistle gets its name from the milky fluid that comes out of the leaves when they are broken.
Silymarin is a lipophilic extract from the seeds (most concentrated in the fruit and seeds) of the milk thistle plant and is believed to be the biologically active part of the herb. Silymarin is prescribed in case of cirrhosis, viral hepatitis and Amanita phaloides (Death Cap) poisoning. Silybin is a component with the greatest degree of biological activity and makes up 50 to 70% of silymarin.
Milk Thistle as Liver Detox – Can Milk Thistle Benefit for Liver Diseases?
Andrea Rambaldi et al.  wanted to assess the beneficial and harmful effects of milk thistle versus placebo. They reviewed 13 randomized clinical trials in 915 patients with alcoholic and/or hepatitis B or C virus liver diseases. Their results question the beneficial effects of milk thistle for patients with alcoholic and/or hepatitis B or C virus liver diseases and report the lack of high-quality evidence. They concluded that milk thistle versus placebo has no significant effect on mortality, complications of liver disease, or liver histology. Low-quality trials suggested beneficial effects, but not high-quality trials. Studies show no significantly increased risk of adverse effects.
Many previous studies show that milk thistle may benefit the liver by protecting and promoting the growth of liver cells and fighting oxidation. However, most of recent and strictly conducted studies contrast these claims. For example, a 2012 clinical trial , cofounded by NCCAM and the National Institute of Diabetes and Digestive and Kidney Diseases, showed that two high doses of silymarin were no better than placebo for chronic hepatitis C.
One retrospective study  (a survey of 1,145 participants) found that silymarin use by people with hepatitis C was associated with fewer symptoms and somewhat better quality-of-life, but there was no change in virus activity or liver inflammation.
Despite negative reports, milk thistle seems to have some effect in chronic liver diseases, particularly alcohol related liver disease, toxin-induced liver disease, and viral liver disease .
Milk Thistle and Female Fertility
Milk thistle can purportedly aid in female fertility. There are no studies to directly measure these claims. However, milk thistle plant extract (but not seed extract) might enhance the effects of estrogen . Milk thistle extract (containing silibinin) has been shown to be effective in preventing estrogen deficiency-induced bone loss in preclinical trial .
Due to its effect on estrogen, hormone-sensitive conditions such as breast cancer, uterine cancer, endometriosis or uterine fibroids may be worsened.
Milk Thistle Side Effects
Milk thistle has shown few side effects in clinical trials and is generally well tolerated. According to Medline Plus  : “Milk thistle is likely safe for most adults. Milk thistle sometimes causes a laxative effect. Other less common side effects are nausea, diarrhea, indigestion, intestinal gas, bloating, fullness or pain, and loss of appetite.”
(Other common names: Silymarin, Silymarine, St. Mary Thistle, St. Marys Thistle, Our Lady’s Thistle, Shui Fei Ji, Silibinin, Silybe de Marie, Silybin, Silybum, Silybum marianum, Holy Thistle, Lady’s Thistle, Lait de Notre-Dame, Legalon, Marian Thistle, Mariendistel, Mary Thistle, Artichaut Sauvage, Blessed Milk Thistle, Thisilyn)
- Abenavoli, Ludovico, et al. “Milk thistle in liver diseases: past, present, future.” Phytotherapy Research 24.10 (2010): 1423-1432.
- Rambaldi, A., B. P. Jacobs, and C. Gluud. “Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases.” Cochrane Database Syst Rev 4 (2007).
- National Center for Complementary and Alternative Medicine. Hepatitis C: A Focus on Herbal Supplements – Retrieved 15. April 2013
- Seeff LB, et al. Herbal product use by persons enrolled in the hepatitis C antiviral long-term treatment against cirrhosis (HALT-C) trial. Hepatology. 2008;47(2):605–612
- Medline Plus. Milk thistle. http://www.nlm.nih.gov/medlineplus/druginfo/natural/138.html Retrieved 15. April 2013
- Tamayo, Carmen, and Suzanne Diamond. “Review of clinical trials evaluating safety and efficacy of milk thistle (Silybum marianum [L.] Gaertn.).” Integrative cancer therapies 6.2 (2007): 146-157.
- Kim, Jung-Lye, et al. “Antiosteoclastic activity of milk thistle extract after ovariectomy to suppress estrogen deficiency-induced osteoporosis.” BioMed research international 2013 (2013).