Milk thistle (Silybum marianum) contains silymarin, which is a mixture of flavonolignans, mainly silibinin (also known as silybin), as well as silycristine, silydianin, quercetin and taxifolin. Silymarin is a standardized preparation extracted from the fruits (seeds) of milk thistle. Milk thistle is a purported galactogogue, and is included in some proprietary mixtures promoted to increase milk supply; however, no scientifically valid clinical trials support this use.[3-5] Although a study on the high potency purified milk thistle component, silymarin, and a phosphatidyl conjugate of silymarin indicated some galactogogue activity, this does not necessarily imply activity of milk thistle itself. Galactogogues should never replace evaluation and counseling on modifiable factors that affect milk production.[6,7]
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. Mothers taking milk thistle to increase milk supply reported weight gain, nausea, dry mouth and irritability occasionally. Milk thistle might increase the metabolism of some drugs. 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 U.S. 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 information about dietary supplements is available elsewhere on the LactMed Web site.