Natural Antioxidant—Great for Liver Health

Is Milk Thistle Safe?

What are the possible side effects of milk thistle?

Milk thistle is generally considered safe, even when taken for years.(9)

Some possible side effects include:(93645)

  • Constipation or diarrhea
  • Nausea
  • Nosebleed
  • Skin rash
  • Stomachache
  • Vomiting
Milk Thistle Table 3: Specific Safety Concerns
Potentially Unsafe Effect Details

May cause metabolic issues or interfere with brain development.(46)

Lab studies show that silymarin extracts from milk thistle significantly block the uptake of thyroid hormones into cells. In particular, milk thistle's silycristin compounds are particularly potent inhibitors of thyroid hormone uptake by cells.(46)

Although most supplements are sold as milk thistle or silymarin extracts, dosing studies in humans these could still be concerning. Why? Blood tests show a single 600 mg dose of milk thistle extract results in a level of silycristin that may interfere with thyroid hormone uptake.(46)

Allergic reaction.(36)

Milk thistle is in the same plant family as ragweed.(36)

If you're allergic to kiwi, you may want to avoid milk thistle. There is one case report of a man going into anaphylactic shock after drink an herbal tea containing milk thistle. He was also found to be allergic to kiwi fruit.(230)

Could interfere with losartan, a common drug for high blood pressure.(47)

In a small clinical trial, 420 mg/day of silymarin (for 2 weeks) inhibited metabolism of losartan.(47)

Increased levels of talinolol, a beta blocker heart medication.(47)

When tested in healthy subjects, 420 mg/day of silymarin for 14 days significantly increased the peak concentration of talinolol in the blood.(47)

Blocks warfarin.(47)

Lab studies suggest silybin A and silybin B both potently inhibit warfarin metabolism.(47)

Decreased effectiveness of nystatin, an antifungal drug.(48)

According to lab studies, silymarin compounds reduced the effectiveness of nystatin against several Candida yeast species.(48)

Is Milk Thistle Safe for Pregnant or Nursing Women?

Some integrative medical doctors recommend that pregnant or breastfeeding women avoid taking milk thistle. However, research suggests taking milk thistle supplements may be beneficial for breastfeeding.(454950)

Milk thistle extract may also be beneficial as an anti-inflammatory in pregnant women with pre-eclampsia - at least on the cellular level. In clinical studies, no harmful effects were found to either the mothers or babies.(49-51)

Milk Thistle Table 4: Research Studies Involving Pregnant or Nursing Women
Clinical Study Details Key Findings

50 breastfeeding women(49)

Participants were assigned to take either 420 mg/day of milk thistle silymarin extract or placebo for 63 days.(49)

Those who took the milk thistle supplements produced significantly more breast milk than those who took placebo.(49)

The milk thistle did not adversely change the chemical composition of the breast milk.(49)

3 groups:(50)

  • 34 pregnant women with pre-eclampsia
  • 20 pregnant women with normal blood pressure
  • 15 non-pregnant women

Silibinin from milk thistle significantly reduces high levels of inflammatory proteins found in blood from women with pre-eclampsia.(50)

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Micronized silymarin product BIO-C®.(49)