Milk thistle has been recognized for its potential health benefits for thousands of years, but its use as a supplement became widely popular only recently. In the United States, sales of milk thistle supplements reached an impressive $95 million in 2008, and by 2022, the global market had soared to over $1 billion, according to one study.

While this rapid growth is a positive development for manufacturers and marketers of milk thistle supplements, many potential users remain uncertain about the actual advantages of taking this product in its various forms.

Below are the pros and cons of using milk thistle supplements, alongside insights on their safety.

What is milk thistle?

Originally from Europe, milk thistle is now also widespread in the United States. It belongs to the daisy (Asteraceae) family, which includes over 30,000 species like sunflowers, dahlias, and marigolds.

Milk thistle features vibrant magenta or purple flowers and large, spiky leaves. When crushed, these leaves release a milky white sap, which is how the plant got its name, explains nutritional scientist and registered dietitian Perri Halperin. However, this sap is rarely consumed; instead, the active ingredient known as silymarin is extracted from the seeds of the plant.

These extracts are processed into a dietary supplement that can be taken in various forms, such as pills, powders, tinctures, or liquids, according to nutritionist Amy Goodson.

Is milk thistle beneficial? Is it helpful for liver issues?

Despite numerous claims and suggested health benefits, we have limited evidence on whether milk thistle can genuinely enhance health conditions or overall wellness. According to the U.S. National Institutes of Health National Center for Complementary and Integrative Health (NCCIH), only a few rigorously conducted clinical trials exist.

That said, the antioxidant properties of milk thistle are thought to potentially improve skin problems like acne and dryness, lower cholesterol levels, and even enhance immune function, says Vanessa Rissetto, a registered dietitian at Culina Health. “Emerging studies suggest it might assist in managing blood sugar levels, but further research is essential to back this up,” Goodson adds.

Additionally, milk thistle is often marketed towards those looking for liver support, such as individuals with liver diseases or heavy alcohol consumption history. A 2017 meta-analysis indicated a “marginal reduction” in liver disease severity for patients taking milk thistle. It is believed to support liver function by inhibiting toxins from binding to the liver, though this is unproven, according to Halperin.

Halperin also notes that some laboratory studies hint that silymarin in milk thistle may exhibit anti-cancer properties, such as slowing the growth of cancer cells and reducing their longevity, but again, more investigations are needed.

One of the more well-established and perhaps surprising applications of milk thistle is its use as an emergency treatment for mushroom poisoning. “Some animal research has shown that milk thistle can negate the toxic effects of poisonous mushrooms if administered within 10 minutes of ingestion,” Halperin explains.

Is milk thistle safe to use?

According to the NCCIH, milk thistle supplements are generally regarded as safe and well-tolerated when taken as recommended. However, Goodson advises that excessive intake may lead to side effects such as bloating, gas, diarrhea, or nausea.

Rissetto warns that individuals with diabetes should be cautious when considering milk thistle, as it can influence blood sugar levels. Additionally, those with allergies to ragweed, chrysanthemums, marigolds, chamomile, or daisies should avoid it, Halperin cautions.

It’s also important to be aware that the supplement may interact with medications that are processed by the liver, including certain blood thinners and cholesterol-lowering drugs. Goodson recommends consulting with a healthcare provider before start using milk thistle.