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According to 2019 literature, silymarin is safe in doses of up to 700 mg three times per day.
Side effects may include:
- • Diarrhea
- • Nausea
- • G.I. discomforts
- • Allergies in those allergic to the Asteraceae family (daisies, marigolds, chrysanthemums)
- • Rashes
Use in pregnancy is not discouraged and no anomalies have historically been cited. Even so, caution should be exercised during pregnancy and breastfeeding.
Drug-Nutrient Interactions
There is some confusion as to drug-nutrient interactions, but moderate interactions may exist for some drugs such as diabetes medication, morphine sulphate, valium, chemotherapy drugs and others with a narrow therapeutic window. Whereas milk thistle may act to help lower blood sugar and yield better control, it may also lead to a hypoglycemic event in someone on oral hypoglycemic agents who take milk thistle concurrently without blood sugar monitoring, for example. *
Adverse Reactions
In most clinical trials, the incidence of adverse reactions was approximately equal in milk thistle and control groups. The US Agency for Healthcare Research and Quality and the German Commission E reported no serious adverse events associated with milk thistle within the recommended dosage range.
Silymarin is well tolerated; the most common effects after oral ingestion were brief GI disturbances (eg, abdominal bloating, abdominal fullness or pain, anorexia, changes in bowel habits, diarrhea, dyspepsia, flatulence, nausea). Headache and pruritus have also been reported. A tea made from crude milk thistle resulted in a case report of anaphylaxis. High dosages in cancer trials have been associated with asymptomatic hyperbilirubinemia and increases in ALT enzymes.
A case report describes a 57-year-old woman with a 2-month history of intermittent episodes of sweating, nausea, colicky abdominal pain, diarrhea, vomiting, and weakness/collapsing. She recalled taking milk thistle for headaches and liver cleansing for about 2 months. Upon further questioning and cessation, it was determined that milk thistle was related to her symptoms.
Toxicology
Avoid use of the aboveground parts of the plant in women with hormone-sensitive conditions (eg, breast, uterine, and ovarian cancers; endometriosis; uterine fibroids), unless under the supervision of a physician, due to the extract's possible estrogenic effects. The more commonly used milk thistle seed extracts are not known to have estrogenic effects.
Oral consumption of milk thistle (standardized to 70% to 80% silymarin) at 420 mg/day is considered safe for up to 41 months based on clinical trial data. Acute oral toxicity of silymarin in rats, dogs, and monkeys has been estimated at dosages greater than 5 g/kg. Subacute toxicity studies suggest no toxicity in rats and monkeys at dosages up to 2 g/kg for 13 weeks, and up to 1 g/kg in rats and dogs for up to 26 weeks. Investigations, including urine analysis and postmortem studies, showed no evidence of toxicity. No evidence of effect on reproduction in rats has been found, and silymarin was not mutagenic in several tests.
Toxic effects of silymarin have not been noted clinically at a dosage of 1,200 mg/day; however, mild allergies were reported with dosages greater than 1,500 mg/day. *
