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:
Endometrial cancer is a disease that primarily affects postmenopausal women at an average age of 60 years at diagnosis. Risk factors include postmenopausal estrogen therapy, obesity, a high-fat diet, reproductive factors like nulliparity, early menarche and late menopause, polycystic ovarian syndrome, and tamoxifen use. Women with hereditary nonpolyposis colorectal cancer syndrome have a markedly increased risk of endometrial cancer compared with women in the general population.
In stimulating detoxification pathways (enzyme concentrations and activity).
For antioxidant properties.
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),[1,2,3,4,5,6]breast (MDA-MB 468, MCF-7),[7,8,9]hepatic (HepG2),[10,11] epidermoid (A431),colon (Caco-2),ovarian (OVCA 433, A2780),histiocytic lymphoma (U-937), and leukemia (HL-60) [15,16]cells. In animal tumor models, tongue cancer, skin cancer,[18,19,20,21,22,23]bladder cancer, and adenocarcinoma of the colon [25,26] and small intestine  have been investigated. These studies have tested the ability of silymarin or silibinin to:
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.[11,27,28,29,30,31] 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]