Silymarin is generally considered a safe and well-tolerated supplement.
Some reported side effects include dry mouth, mild gastrointestinal symptoms (e.g., nausea, irregular stools, dyspepsia, diarrhea), headaches, and allergic reactions. However, the frequency of occurrence of such adverse events remains unclear, and a direct attribution to silymarin has not yet been confirmed.[1][2][3]
Additionally, in studies on cancer patients, asymptomatic mild liver toxicity has been observed at very high dosages of silymarin (between 10 and 20 grams per day).[2]
However,the safety of silymarin during pregnancy and breastfeeding has not been established; more research is needed, and its use is therefore not recommended during pregancy and breastfeeding.[1]
Finally, although in vitro studies have suggested potential interactions between silymarin and medications metabolized by some enzymes in the cytochrome P450 family, particularly CYP3A4 and CYP2C9 (the latter of which is involved in warfarin’s metabolism, for example), clinical trials have not yet confirmed these findings.[3]