Milk Thistle

Drug Levels and Effects:

Summary of Use during Lactation:

Milk thistle (Silybum marianum) contains silymarin which is a mixture of flavonolignans, mainly silibinin (also known as silybin). Silymarin is a standardized preparation extracted from the fruits (seeds) of milk thistle. Milk thistle is a purported galactogogue,[1][2] and is included in some proprietary mixtures promoted to increase milk supply; however, no scientifically valid clinical trials support this use. Galactogogues should never replace evaluation and counseling on modifiable factors that affect milk production.[3] Limited data indicate that the silymarin components are not excreted into breastmilk in measurable quantities. Additionally, because silymarin components are poorly absorbed orally, milk thistle is unlikely to adversely affect the breastfed infant. Milk thistle and silymarin are generally well tolerated in adults with only mild side effects such as diarrhea, headache, and skin reactions. Rarely, severe allergies and anaphylaxis are reported. Avoid in patients with known allergy to members of the aster (Compositea or Asteraceae) family, such as daisies, artichokes, common thistle, and kiwi because cross-allergenicity is possible.

Dietary supplements do not require extensive pre-marketing approval from the US Food and Drug Administration. Manufacturers are responsible to ensure the safety, but do not need to prove the safety and effectiveness of dietary supplements before they are marketed. Dietary supplements may contain multiple ingredients, and differences are often found between labeled and actual ingredients or their amounts. A manufacturer may contract with an independent organization to verify the quality of a product or its ingredients, but that does not certify the safety or effectiveness of a product. Because of the above issues, clinical testing results on one product may not be applicable to other products. More detailed informationabout dietary supplementsis available elsewhere on the LactMed Web site.

Drug Levels:

Silibinin has low and variable bioavailability of 23 to 47% after oral administration and is rapidly converted into glucuronide conjugates which have longer half-lives in plasma than the unconjugated forms.[4]

Maternal Levels.

Five mothers who had decided to stop nursing because their infants were 9 months old were given 600 mg of micronized silymarin (BIO-C brand) orally 3 times daily. After 5 days of therapy, milk was collected at unspecified times for analysis by HPLC. Silymarin flavonolignans were undetectable (<1 mcg/L) in milk samples; however, their conjugated forms might not have been detected by the assay method used.[5]

Infant Levels.

Relevant published information was not found as of the revision date.

Effects in Breastfed Infants:

Relevant published information was not found as of the revision date.

Possible Effects on Lactation:

A study was performed on 50 medically normal postpartum mothers with milk production judged to be less than normal for patients in the hospital in Lima,Peruwhere the study was conducted. Mothers were divided non-randomly into 2 groups of 25 women who had identical ages, weights, number of children and newborn's age, although ages were not reported. The group that was given micronized silymarin (BIO-C brand) 420 mg daily for 63 days had a baseline milk production of 602 mL daily. The milk volumes and composition (water, fats, carbohydrate and protein) of the 2 groups were not significantly different on day 0. The group given an identical placebo had a baseline milk production of 530 mL daily. Milk production was measured on day 30 and day 63 by infant weighings before and after nursing followed by emptying the breasts with a breast pump. The composition of the milk was also determined. Statistically significant differences in average milk production were found on day 30 (990 grams in the silymarin group and 650 grams in the placebo group) and on day 63 (1119 grams in the silymarin group and 701 grams in the placebo group). Milk composition was not different between the groups at the two time points.[5] Deficiencies in this study include the lack of randomization, no investigator blinding, and no optimization of breastfeeding technique prior to study enrollment. Also, breastfeeding duration and long-term infant growth were not studied.


1. Jackson PC. Complementary and alternative methods of increasing breast milk supply for lactating mothers of infants in the NICU. Neonatal Netw. 2010;29:225-30. PMID:20630837
2. Abascal K, Yarnell E. Botanical galactagogues. Altern Complement Ther. 2008;14:288-94.
3. The Academy of Breastfeeding Medicine Protocol Committee. ABM clinical protocol #9: use of galactogogues in initiating or augmenting the rate of maternal milk secretion (First revision January 2011). Breastfeed Med. 2011;6:41-9. PMID:21332371
4. He SM, Li CG, Liu JP et al. Disposition pathways and pharmacokinetics of herbal medicines in humans. Curr Med Chem. 2010;17:4072-113. PMID:20939821
5. 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;79:205-10. PMID:19260380

Substance Identification:

Substance Name:

Milk Thistle

Scientific Name:

Silybum marianum

CAS Registry Number:

65666-07-1 84604-20-6 22888-70-6

Drug Class:

  • Antioxidants

  • Complementary Therapies

  • Galactogogues

  • Phytotherapy

  • Plants, Medicinal

  • Protective Agents

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

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