Milk thistle has been used for centuries as a natural remedy for liver health, but when it comes to pregnancy, the question of safety becomes more complex. If you are expecting and wondering whether milk thistle is safe to take, this article breaks down what the current research says and what precautions you should consider.
What Is Milk Thistle Extract?
Milk thistle (Silybum marianum) is a flowering plant in the Asteraceae family, native to the Mediterranean region. Its active compound, silymarin, is a standardized extract derived from the plant's seeds. Milk thistle extract is widely used in dietary supplements for its antioxidant and hepatoprotective properties. The extract is typically standardized to contain 70% to 80% silymarin, which is the component most studied in clinical research.
If you are asking what is milk thistle extract used for, the answer spans from liver support to metabolic health. It has been studied for conditions such as alcoholic liver disease, non-alcoholic fatty liver disease, and even as a supportive agent during certain drug therapies. However, its use during pregnancy requires a closer look at the available evidence.
Is Milk Thistle Safe During Pregnancy?
The short answer is that there is insufficient high-quality human data to definitively state that milk thistle is safe during pregnancy. While some limited studies have not shown harmful effects, most health authorities and guidelines recommend exercising caution.
According to the 2023 guidelines from the European Association for the Study of the Liver (EASL) on liver diseases in pregnancy, healthcare providers should obtain a careful history of herbal products when evaluating unexplained liver test elevations in pregnant women. This recommendation indirectly highlights the need for vigilance with any herbal supplement during pregnancy.
A 2025 Cochrane review that analyzed data from over 2,000 participants confirmed that silymarin results in little to no difference in serious adverse events compared to placebo in the general adult population. However, the review noted that the certainty of evidence ranges from low to very low, and most safety data comes from studies lasting 4 to 48 weeks — meaning long-term safety data beyond one year remains limited.
What Does the Research Say?
Here is a summary of the key findings from the available scientific literature on milk thistle use during pregnancy:
- Animal studies show promise: A 2020 study published in Neurotoxicology examined silymarin administration during pregnancy and breastfeeding in mice. The researchers found no morpho-functional changes in offspring, suggesting no developmental harm at the doses tested.
- One human clinical trial: A clinical trial reported no anomalies with silymarin use during pregnancy, but this was a single study and does not constitute sufficient evidence for broad safety recommendations.
- No reports of estrogenic effects: Given that milk thistle contains flavonolignans, there has been theoretical concern about estrogenic effects on the fetus. However, no such effects have been reported in the available literature.
- Limited sample sizes: Most studies on milk thistle in pregnancy involve small numbers of participants, making it difficult to draw firm conclusions about safety for the general pregnant population.
Key takeaway: The limited evidence available does not point to clear harm, but it is also not robust enough to recommend milk thistle as safe for routine use during pregnancy. Always consult your healthcare provider before taking any supplement while pregnant.
Milk Thistle and Breastfeeding
The picture is somewhat different for breastfeeding. Milk thistle has been studied as a potential galactogogue — a substance that may help increase breast milk production. Several clinical trials have examined silymarin's effects on lactation:
- A study involving 50 postpartum mothers in Peru found that those who took micronized silymarin (420 mg daily) produced significantly more breast milk at day 30 and day 63 compared to the placebo group (990 g vs. 650 g and 1,119 g vs. 701 g, respectively).
- However, a more recent randomized controlled trial on mothers of preterm infants found no significant difference in milk production between silymarin and placebo groups, leading to a conclusion of "very low certainty evidence" for silymarin as a galactogogue.
- Importantly, silymarin components were not detected in breast milk at measurable levels in multiple studies, and no adverse effects were observed in breastfed infants.
The LactMed database (revised March 2026) notes that milk thistle is "unlikely to adversely affect the breastfed infant" due to poor oral absorption of silymarin components, though it emphasizes that galactogogues should never ｒｅｐｌａｃｅ evaluation and counseling on modifiable factors that affect milk production.
Potential Risks and Side Effects
While milk thistle is generally well tolerated in adults, it is important to be aware of the following considerations:
- Mild gastrointestinal effects: Some users report nausea, diarrhea, bloating, or mild stomach discomfort.
- Allergic reactions: People with known allergies to plants in the Asteraceae family (such as daisies, ragweed, artichokes, and chrysanthemums) should avoid milk thistle due to the risk of cross-allergenicity.
- Drug interactions: Silymarin can interact with CYP450 enzymes in the liver, potentially affecting how the body metabolizes certain medications, including some anticoagulants and anti-seizure drugs. If you are taking any prescription medication during pregnancy, discuss milk thistle use with your doctor.
- Blood sugar effects: Milk thistle may lower blood sugar levels, which is relevant for women with gestational diabetes.
The Bottom Line: Should You Take Milk Thistle While Pregnant?
Based on the current body of evidence, the most prudent approach is to avoid milk thistle supplements during pregnancy unless specifically recommended by your healthcare provider. The limited human data, while not showing clear harm, does not provide the level of certainty needed to ｄｅｃｌａｒｅ milk thistle safe for routine use during this critical period.
If you are considering milk thistle for a specific health concern during pregnancy, have an open conversation with your obstetrician or midwife. They can help you weigh the potential benefits against the unknowns and may suggest alternative approaches with better-established safety profiles.
For those who are not pregnant and are interested in the broader milk thistle extract benefits — including liver support, antioxidant protection, and metabolic health — milk thistle remains one of the most widely studied and well-tolerated botanical supplements available on the market today.
Looking for high-quality milk thistle extract?
Cactus Botanics supplies standardized milk thistle extract with 80% silymarin (UV), produced under GMP-compliant manufacturing with full batch traceability and analytical testing.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. The statements in this article have not been evaluated by the U.S. Food and Drug Administration. Milk thistle products are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before taking any supplement, especially during pregnancy or breastfeeding.
