Milk Thistle in pregnancy and breastfeeding

What NCCIH says about safety

Milk thistle, when taken orally, appears to be well tolerated. The most common side effects are digestive symptoms such as bloating, nausea, and gas. Concerns have been raised about poor chemical and microbiological quality of milk thistle dietary supplements sold in the United States and other countries. Some products have been found to contain amounts of silymarin substantially different from what’s stated on the label or to be contaminated with pesticides, microorganisms, or mycotoxins (harmful substances produced by molds or other fungi). Milk thistle may cause allergic reactions, particularly among people who are allergic to related plants (for example, ragweed, chrysanthemum, marigold, and daisy). If you take any type of medicine, talk with your health care provider before using milk thistle or other herbal products; some herbs and medicines interact in harmful ways. Little is known about whether it’s safe to use milk thistle during pregnancy or while breastfeeding.

Quoted in full from NCCIH so nothing is lost in summarising. Where they say “little is known”, that means the studies do not exist — not that the herb is known to be safe, and not that it is known to be harmful.

How much is actually known

There isn’t enough high-quality evidence to allow definite conclusions to be reached about the effects of milk thistle on health conditions in people.

What the research has found

Results from a small number of studies in people show that milk thistle extracts may help to control blood sugar in people with type 2 diabetes. Most of this research was done in Middle Eastern countries, and it is unclear whether the same results would be seen in other parts of the world. Results from clinical trials of milk thistle for liver diseases, such as alcohol-related liver disease, hepatitis B and C, non-alcoholic fatty liver disease, and liver problems caused by cancer chemotherapy, low oxygen levels, or toxins have been conflicting or too limited to allow conclusions to be reached. Two studies funded by the National Center for Complementary and Integrative Health—one on hepatitis C and one on non-alcoholic steatohepatitis (a progressive form of fatty liver disease)—did not show benefits from supplementation with the milk thistle extract silymarin. It is unclear whether milk thistle has an effect on breast milk production. It’s not known whether milk thistle is helpful for other conditions.

Before you take this

Dose and form change the answer completely. A culinary amount of a spice, a cup of tea, and a concentrated supplement extract are three different things, and most research is done on the last of them.

Supplements are also not regulated like medicines, so strength and purity vary between products. Bring the actual bottle to your midwife, doctor or pharmacist — that conversation is worth more than any page, including this one.