Milk Thistle (Silymarin): Benefits and Side Effects - Vitamin & Herbal Supplements

Milk Thistle (Silymarin): Benefits and Side Effects

A short, wide, prickly plant known as milk thistle (Silybum marianum) is the source of a popular herbal remedy that is widely used to support healthy liver function.

Milk thistle is an invasive species that, ironically, can be toxic to grazing cattle. The seeds, however, are another matter. They contain a complex of “flavonolignan” (part flavonoid, part lignan) compounds, silibinin, silidianin, and silicristin, that are collectively known as “silymarin.”

Silymarin and its components show great therapeutic promise, and are the subjects of ongoing research and clinical trials.

Studies have confirmed that the active components in milk thistle have hepatoprotective effects—that is, they can help protect the liver from damage from toxic or disease-causing agents.

Animal experiments have shown, for example, that milk thistle/silymarin administration can reduce liver damage from acetaminophen (Tylenol), excess iron, alcohol and carbon tetrachloride.

In addition, animal models suggest milk thistle and/or its components could alleviate oxidative stress and reduce memory impairments associated with Alzheimer’s disease.

Silymarin may exert other neuroprotective effects, as well as promote skin health: topical silymarin was found to reduce skin damage from experimental burns and inhibit photocarcinogenesis induced by UV radiation.

Some human data has also been collected on patients with cirrhosis and hepatitis, although the results have been mixed. In addition, a recent clinical trial concluded that milk thistle may reduce the liver toxicity associated with cancer chemotherapy.

Lastly, silymarin appears to be beneficial in cases of Amanita phalloides poisoning.

What about milk thistle for healthy people? It’s often touted as a hangover cure, a “detox” or “cleansing” agent, and an adjunct to anabolic steroid/prohormone use.

Unfortunately, there’s only anecdotal evidence in support of these uses.

Milk thistle can be purchased in a variety of forms. The active ingredients can be extracted with alcohol to produce a tincture, or pills can be prepared using the seeds.

Milk thistle teas made from bulk seed are also available, but very little of the active ingredients are present in steeped teas.

Potential users should also be aware that quality-control can be an issue with milk thistle supplements—an independent test by Consumer Labs revealed that the majority of products sampled were low in the active ingredients.

Few side effects have been reported from the use of milk thistle seed extract, though capsules or tablets can sometimes cause stomach irritation. A mild laxative effect has been reported as well, but this is often a desired effect of treatment.

Despite its relative safety, the usual cautions apply for pregnant/nursing women and those taking prescription drugs. In particular, people taking certain allergy medications, statins, anti-anxiety drugs or blood-thinners should consult with their healthcare providers before using milk thistle.

Silymarin is available online from, one of our recommended online retailers.

Author: elissa

Elissa is a former research associate with the University of California at Davis, and the author/co-author of over a dozen articles published in scientific journals. Currently a freelance writer and researcher, Elissa brings her multidisciplinary education and training to her writing on nutrition and supplements.

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