Milk Thistle for Breast Milk: 2 Trials of the Same Extract, Opposite Results

Quick Answer: Milk thistle has been tested on its own for breast milk supply in two placebo-controlled trials that we could find in PubMed, and both used the same product: a micronized extract called BIO-C, taken at 420 mg a day by 50 mothers per trial. In the first, from 2008, milk output rose 85.94% on the extract against 32.09% on placebo. In the second, from 2015, in mothers of very premature babies, there was no difference: the extract group’s output rose 24.9 g a day and the placebo group’s 77.3 g a day (P=0.872). The Academy of Breastfeeding Medicine rates the evidence “inconclusive” and recommends no specific galactagogue, and the US National Center for Complementary and Integrative Health (NCCIH) says “little is known” about its safety while breastfeeding. Most other studies of milk thistle and milk production were done in cows, sows and ewes.

This page is about one question: does milk thistle raise breast milk supply, and is it safe to try while nursing or pregnant. For the other uses of the plant, from fatty liver to blood sugar, see our review of seven milk thistle uses.

Milk thistle for breast milk: every human trial we found

Two of those five studies tested milk thistle alone. The other three added a second herb, galega, which has its own reputation as a milk booster, so they cannot tell you what milk thistle contributed.

Same extract, same dose, opposite results

The two single-herb trials are unusually easy to compare, because they gave the same branded extract at the same daily amount to groups of the same size.

The positive trial. In 2008, Di Pierro and colleagues gave 50 healthy breastfeeding women either micronized silymarin at 420 mg a day or a placebo described as “undistinguishable”, for 63 days. Daily milk production rose 85.94% on silymarin and 32.09% on placebo. The authors concluded that silymarin “may be considered as a safe and effective herbal product” for raising milk production. The abstract opens by noting that the authors had “previously reported the use of Silymarin … as a promoter of milk production in cows”, and the first author’s listed affiliation is Velleja Research in Pontenure, Italy.

The null trial. In 2015, a neonatology team at the University of Turin ran a double-blind trial in 50 mothers whose babies had been born before 32 weeks. The manufacturer of BIO-C prepared identical sachets of the extract (420 mg dry extract, corresponding to 252 mg of micronized silymarin a day) and of maltodextrin placebo. Mothers recorded every pumping session or weighed their babies before and after feeds. The study’s own summary: “No differences emerged in milk production profile between the silymarin BIO-C and placebo arms.”

The numbers behind that sentence point the other way from what the label promises. Between the start of treatment and days 26 to 28, the main measure, production rose 24.9 g a day in the silymarin group and 77.3 g a day in the placebo group, a difference of minus 52.4 g a day that was not statistically significant (P=0.872). The silymarin group also started with more milk, which the authors attribute to more of those mothers having breastfed before. The paper discloses support from the Iolanda Minoli Foundation and from Milte Italia S.r.l.

Two further findings from the Turin trial matter to a nursing mother. Neither group reported side effects in mothers or babies, and “silymarin and its metabolites were not detectable in the analyzed human milk samples.” That second result is reassuring about exposure for the baby, but it is one small trial.

Why the two trials might disagree

The two trials studied different mothers. Di Pierro enrolled healthy women after an ordinary delivery. Peila enrolled mothers of babies born before 32 weeks, a group the authors describe as often having difficulty “maintaining a sufficient production of milk for their infants’ needs over prolonged periods of time.” A herb could plausibly help one group and not the other.

But the placebo results show how fragile any single small trial is here. In the 2008 trial, milk output rose by almost a third on placebo alone. In 2015, the placebo group’s increase was larger than the silymarin group’s. Milk supply in the early weeks rises and falls for reasons that have nothing to do with a capsule: how often milk is removed, how well the baby feeds, sleep, stress and the baby’s own health. The Academy of Breastfeeding Medicine’s protocol says plainly that medication “should never replace evaluation and counseling on modifiable factors.”

Only one of the two trials has been checked by a team without a stated link to the product’s development, and that is the one that found nothing. No trial of milk thistle for lactation appears in the US ClinicalTrials.gov registry; our search on 3 November 2026 for silymarin or milk thistle with lactation, breastfeeding or breast milk returned no lactation studies.

Where the “milk thistle raises prolactin” idea comes from

The proposed mechanism is that milk thistle raises prolactin, the hormone that drives milk production. The study usually behind that claim was done in rats. In 2009, a pharmacology team in Naples gave female rats the same BIO-C extract at 25 to 200 mg per kilogram of body weight for 14 days and found that blood prolactin rose with the dose. That is a rat dose many times above the human one, and no human trial we found measured prolactin.

Animal work dominates the field more broadly. A PubMed search on 3 November 2026 combining milk thistle, silymarin or Silybum with lactation, breast milk, galactagogues or breastfeeding returned 36 records. Sixteen of them are studies in sows, dairy cows, ewes, dairy sheep, rats or mice, many of them about livestock productivity. That is where milk thistle’s reputation as a milk booster has the most data behind it, and it is not data about women.

What the reviews and guidelines say

Cochrane, 2020. A Cochrane review of galactagogues for mothers of healthy term babies included 41 randomised trials and 3,005 mothers. Silymarin was one of 13 natural products with milk volume data, but the results were too different from each other to pool (heterogeneity I² = 99%). The authors were “very uncertain” about the size of any effect of natural galactagogues and called for “high-quality RCTs on the efficacy and safety of galactagogues.”

Academy of Breastfeeding Medicine, 2018. The ABM’s galactagogue protocol rates the evidence for silymarin as “Inconclusive. Possible increase in milk secretion in the short term”, lists it as generally well tolerated with occasional mild stomach upset, and warns of cross-allergy with the daisy family. Its overall position: “ABM cannot recommend any specific galactogogue at this time.”

Preterm mothers, 2026. A systematic review of herbal galactagogues for mothers of premature babies found ten randomised trials, each testing something different. It rated the evidence for the silymarin-plus-galega product as “low certainty” (an average of 105 ml more by day 7, with a wide range of 27 to 183 ml) and concluded that “higher-quality trials are needed.”

NCCIH. The US government’s complementary health centre states: “It is unclear whether milk thistle has an effect on breast milk production.”

Is milk thistle safe while breastfeeding?

The honest answer is that nobody has studied it well enough to say. NCCIH: “Little is known about whether it’s safe to use milk thistle during pregnancy or while breastfeeding.” A 2015 review of nine popular herbal supplements in breastfeeding women, milk thistle among them, concluded that they “have not been evaluated in high-quality clinical trials, and there is limited evidence supporting safety of use, particularly among lactating women.”

What the small trials do tell you:

• No side effects were reported in mothers or babies in either single-herb trial, with 100 mothers between them.
• In the Turin trial, silymarin was not detected in breast milk.
• NCCIH notes that milk thistle “may cause allergic reactions, particularly among people who are allergic to related plants (for example, ragweed, chrysanthemum, marigold, and daisy).”
• NCCIH also warns that supplements have been found to contain amounts “substantially different from what’s stated on the label” or to be contaminated with pesticides, microorganisms or mycotoxins. A baby cannot report a reaction to a contaminant.

Three or four short trials without side effects are not the same as established safety. That is why the major sources stop at “ask your doctor or lactation consultant” rather than giving a green light.

Milk thistle in pregnancy

The pregnancy questions get fewer searches but have even less behind them. We found no trial of milk thistle given to pregnant women to test safety, and NCCIH places pregnancy in the same “little is known” category as breastfeeding. The only pregnancy data on silymarin in our search came from animals: livestock studies in late gestation and a 2020 study in mice. Starting milk thistle “to prepare” for breastfeeding before the birth has no evidence behind it at all.

If your supply is low: what has better evidence

The ABM protocol and the Cochrane review agree on the order of steps. Cochrane: “it is important first to consider the influence of maternal and neonatal health, infant suck, proper latch, and feeding frequency on milk production, and that steps be taken to correct or compensate for any contributing issues.” In practice that means a lactation consultant or doctor looks at how often and how well milk is being removed, and at the health of both mother and baby, before anything is added.

Among drugs, the evidence is stronger than for any herb. Cochrane found “low-certainty evidence that pharmacological galactagogues may increase milk volume”, about 64 ml a day across three trials, and the ABM protocol notes that “a number of high-quality studies have found domperidone to be useful in mothers of preterm infants.” The ABM table lists cardiac risk factors for domperidone, and it is a decision for a doctor, not a pharmacy shelf.

We do not link to any product on this page. With one positive trial, one null trial and no established safety record in nursing mothers, a buy button here would be a recommendation the evidence does not make.

Frequently Asked Questions

Does milk thistle increase breast milk supply?

It is unproven. Two placebo-controlled trials tested the same milk thistle extract at 420 mg a day in 50 mothers each. One, from 2008, found milk output rose 85.94% against 32.09% on placebo; the other, from 2015 in mothers of premature babies, found no difference. NCCIH says it is unclear whether milk thistle has any effect on breast milk production.

How much milk thistle was used in the breastfeeding trials?

Both single-herb trials used a micronized extract called BIO-C at 420 mg a day; the 2015 trial specified that this corresponded to 252 mg of silymarin. The combination trials used 5 g a day of a powder that also contained galega. These are the doses tested, not a recommendation; no dose has been shown to be both effective and safe in nursing mothers.

Is milk thistle safe while breastfeeding?

Not established. NCCIH says little is known about its safety during breastfeeding. The small trials reported no side effects in mothers or babies, and one found no silymarin in breast milk, but the Academy of Breastfeeding Medicine recommends no specific herbal or drug galactagogue. Talk to a doctor or lactation consultant first, especially if you are allergic to ragweed or daisies.

Can you take milk thistle while pregnant?

There are no human safety trials in pregnancy. NCCIH says little is known about whether it is safe during pregnancy, and the only pregnancy data we found on silymarin came from livestock and mice. Ask your obstetric care provider before taking it.

How long does milk thistle take to work for milk supply?

The positive 2008 trial measured over 63 days; the null 2015 trial’s main measure was at days 26 to 28. The combination product with galega showed differences from day 7. Because the single-herb evidence conflicts, there is no reliable answer to how long it takes, or whether it works at all.

Sources

1. Di Pierro F, Callegari A, Carotenuto D, Tapia MM. Clinical efficacy, safety and tolerability of BIO-C (micronized Silymarin) as a galactagogue. Acta Biomed. 2008;79(3):205-10. 50 women, 420 mg/day for 63 days, milk +85.94% vs +32.09% placebo; first author affiliation Velleja Research, Pontenure. PubMed 19260380. Checked 3 November 2026.
2. Peila C, Coscia A, Tonetto P, et al. Evaluation of the galactogogue effect of silymarin on mothers of preterm newborns (<32 weeks). Pediatr Med Chir. 2015;37(3):pmc.2015.105. 50 mothers; BIO-C 420 mg dry extract (252 mg silymarin) vs maltodextrin; change to days 26-28 +24.9 vs +77.3 g/day, difference -52.4 g/day, P=0.872; silymarin not detected in milk; support from the Iolanda Minoli Foundation and Milte Italia S.r.l. Full text read. PubMed 26714778. Checked 3 November 2026.
3. Zecca E, Zuppa AA, D’Antuono A, et al. Efficacy of a galactogogue containing silymarin-phosphatidylserine and galega in mothers of preterm infants: a randomized controlled trial. Eur J Clin Nutr. 2016;70(10):1151-1154. 100 mothers, 5 g/day, 200 vs 115 ml/day. PubMed 27245206. Checked 3 November 2026.
4. Serrao F, Corsello M, Romagnoli C, D’Andrea V, Zecca E. The long-term efficacy of a galactagogue containing sylimarin-phosphatidylserine and galega on milk production of mothers of preterm infants. Breastfeed Med. 2018;13(1):67-69. 45 and 44 mothers responded; exclusive human milk at 3 months 22 vs 12. PubMed 29148822. Checked 3 November 2026.
5. Castoldi F, Pivetti V, Moiraghi L, Marangione P, Lista G. [Silymarin/galega administration in term and preterm mothers to sustain breast feeding: an observational study]. Minerva Pediatr. 2014;66(5):375-80. 16 term and 16 preterm mothers. PubMed 25253186. Checked 3 November 2026.
6. Capasso R, Aviello G, Capasso F, et al. Silymarin BIO-C, an extract from Silybum marianum fruits, induces hyperprolactinemia in intact female rats. Phytomedicine. 2009;16(9):839-44. 25-200 mg/kg for 14 days. PubMed 19303749. Checked 3 November 2026.
7. Foong SC, Tan ML, Foong WC, Marasco LA, Ho JJ, Ong JH. Oral galactagogues (natural therapies or drugs) for increasing breast milk production in mothers of non-hospitalised term infants. Cochrane Database Syst Rev. 2020;5:CD011505. 41 RCTs, 3,005 mothers; natural galactagogue milk volume 13 studies, I² = 99%; pharmacological MD 63.82 ml. PubMed 32421208. Checked 3 November 2026.
8. Brodribb W; Academy of Breastfeeding Medicine. ABM Clinical Protocol #9: Use of Galactogogues in Initiating or Augmenting Maternal Milk Production, Second Revision 2018. Breastfeed Med. 2018;13(5):307-314. Silymarin “Inconclusive”; “ABM cannot recommend any specific galactogogue at this time.” PubMed 29902083; protocol PDF. Checked 3 November 2026.
9. Cragg A, Levene I, Darabi S, Willcox M. Herbal galactagogues to improve breastmilk production and lactation in mothers of preterm babies: a systematic review of clinical trials. Eur J Clin Nutr. 2026;80(2):146-158. 10 RCTs; silymarin with galega MD 105 ml (95% CI 27-183), low certainty. PubMed 41350450. Checked 3 November 2026.
10. Amer MR, Cipriano GC, Venci JV, Gandhi MA. Safety of popular herbal supplements in lactating women. J Hum Lact. 2015;31(3):348-53. Nine herbals including milk thistle. PubMed 25881578. Checked 3 November 2026.
11. National Center for Complementary and Integrative Health. Milk Thistle. Last updated February 2025. nccih.nih.gov. Checked 3 November 2026.
12. PubMed search, 3 November 2026: (silymarin OR “milk thistle” OR silybum) AND (lactation OR “breast milk” OR galactagogue* OR breastfeeding), title/abstract; 36 records, 16 in sows, dairy cows, ewes, dairy sheep, rats or mice. ClinicalTrials.gov search, same date: no lactation trial of silymarin or milk thistle.