Milk Thistle During Pregnancy

My friend has just been diagnosed with aggressive Non-Hodgkins Lymphoma and is 12 weeks pregnant. She has just started chemotherapy and is interested in taking Milk Thistle to protect her liver, but is unsure if it is safe to take while pregnant. Do you know anything about this?

We are not aware of any specific evidence of problems for pregnant women. Milk thistle and its active constituent, silymarin, are considered to be safe, and no adverse reactions other than occasional transient laxative effects have been observed even after long term use.
Edmund Lui wrote in his monograph on milk thistle (in "Herbs, Everyday Reference for Health Professionals", 2000) that the "safety of silymarin in pregnant or lactating women has not been assessed adequately." Silymarin apparently does not have embryotoxic effects, but there is a theoretical concern that its anticancer and "antiproliferative" effects might interfere with normal cell growth in fetuses and infants; and so Dr. Lui advises "caution should be exercised with its use in pregnant and lactating women."