At higher doses a sporadic mild purgative effect may appear.
In recommended doses milk thistle-based products show no harmful effects, even after a long-term usage.1
There are no reports of harmful effects of milk thistle on mother and child during pregnancy, or during breastfeeding. Some sources do not recommend the use of milk thistle during pregnancy and breastfeeding because there are no studies confirming the safety of the herb during those periods. Other sources state that milk thistle may be used during pregnancy and lactation.2
No major negative interactions between milk thistle and other herbs and medicinal products were noted.3