Should People With Breast Cancer Take Milk Thistle?

Key Takeaways:

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  There’s no evidence that milk thistle can treat cancer.

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  Early studies in people suggest that components of milk thistle may help prevent some side effects of chemotherapy and radiation, but more research is needed.

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  Milk thistle is generally considered to be safe, but some experts recommend that people with breast cancer avoid it. Ask your doctor what’s best for you.

Milk thistle is a plant native to the Mediterranean whose fruit and seeds were used to treat liver and bile duct disorders for more than 2,000 years. Today, it’s a popular supplement that people take because they believe it supports liver health and improves diabetes, indigestion, and breast milk production. 

Milk thistle is being studied for its potential to help ease some side effects of chemotherapy and radiation. But there’s no evidence that milk thistle can treat cancer.

Milk thistle is usually taken as a capsule or tablet, but it is also available as a liquid extract. When it is used for skin conditions, it is applied as a topical cream or gel. 

Studies do not usually use whole milk thistle, but its main component, called silymarin. Supplements may be sold as either milk thistle or silymarin.

A small number of studies have found that components of milk thistle can reduce cancer treatment side effects like skin irritation from radiation and damage to the liver and brain from chemotherapy. However, there’s mixed evidence on whether it can help protect the kidneys. These studies have looked at different types of cancer, including breast cancer, colorectal cancer, and acute lymphoblastic leukemia (ALL) in children.

More research in people is needed to know if milk thistle should be recommended to reduce side effects of cancer treatment, but there are some promising early results.

Reducing chemotherapy-induced side effects

Three small studies in people with breast cancer have found that milk thistle and silymarin help protect the liver from chemotherapy-related damage. One of these studies¹ looked at chemo with Adriamycin (chemical name: doxorubicin) and one² with doxorubicin/cyclophosphamide-paclitaxel (AC-T chemo). Another study looked at any type of chemo. 

A few other studies have found that silymarin helps guard against liver damage from chemo for acute lymphoblastic leukemia (ALL) in children and solid cancers generally. 

Whether milk thistle and silymarin can prevent kidney damage is unclear: One study found that silymarin helped protect the kidneys of children with ALL. Both ALL and the chemo used to treat it can damage the kidneys. But another study of adults with a variety of cancers found that taking silymarin did not affect chemo-induced kidney injury.

Small studies in people with a variety of cancers suggest that milk thistle may also:

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  reduce chemotherapy-induced nerve damage, which often affects the hands and feet

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  ease diarrhea and nausea from a chemotherapy combination containing the drug irinotecan, which can damage the intestines (the combination is used to treat colorectal and some other cancers)

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  slow the development and progression of hand-foot syndrome, a skin reaction linked to some types of chemo 

Reducing radiation-induced side effects

Two small studies^3,4 of people with breast cancer who were receiving radiation treatment found that using a topical silymarin cream or gel reduced skin damage.

Radiation often causes a severe infection called mucositis in people with head and neck cancer, but a small study found that taking milk thistle every day delayed the start of the infection and made it less severe.

Effects on cancer growth

There is no evidence that milk thistle can treat cancer in people.

A small study of people with prostate cancer who had their prostate removed found that taking silymarin and selenium daily lowered two markers of prostate cancer, suggesting that the combo slowed progression. But because the two supplements were taken together, it’s impossible to know how silymarin may have contributed to this effect.

Cell and animal studies 

Studies in cells and animals are a key early step in research. But you can’t draw conclusions about how things will work in people based on these studies alone. For example, treating cells in a lab dish with milk thistle won’t tell you how the human body absorbs it or breaks it down. And cancer can behave differently in a mouse than it behaves in a person. These studies are valuable, though, because they help researchers find promising leads and decide if they should test these leads in people.

Additionally, lab studies suggest that compounds in milk thistle may help protect DNA from cancer-causing damage, stop cancer cell growth, kill cancer cells, and boost the effects of some chemotherapy drugs.

Other potential uses

Outside of cancer care, milk thistle has been studied for several other health conditions. A review of 22 studies found that silymarin may help control blood sugar in people with diabetes. It may have similar effects in people with non-alcoholic fatty liver disease.

Milk thistle is generally considered safe for most people, but it may not be appropriate for people with breast cancer. It’s unclear how milk thistle may interact with various cancer treatments, for one.

A couple of studies in rats^5,6 have also found that silymarin can bind to certain estrogen receptors and have some estrogen-like effects. This early research does not show that silymarin causes or fights breast cancer in people. But because milk thistle may act like estrogen or affect estrogen levels, some experts recommend that people who have breast cancer avoid taking it. Ask your doctor what’s best for you.

Milk thistle may cause gastrointestinal side effects like bloating, diarrhea, and stomach upset. In rare cases, some people may have an allergic reaction to it.

For people with a cancer diagnosis who do take silymarin, one study found that 300-450 mg is the optimal dose. But again, it’s unlikely to be recommended for people with breast cancer. Always talk to your doctor before starting a new supplement to ensure it’s safe for you to take.

The bottom line: There’s no evidence that milk thistle can cure or treat cancer, and there’s some concern that it can interfere with cancer treatments and/or estrogen levels. So some experts recommend that people with breast cancer avoid milk thistle. Always talk to your doctor before starting a new supplement, as they’re not safe for everyone.