What Are The Benefits and Side Effects of Milk Thistle?

Written by Emily Halnon
Medically Reviewed by Jabeen Begum, MD on August 04, 2025
6 min read

Milk thistle (silymarin) is a flowering herb related to the daisy and ragweed family. It is native to Mediterranean countries. Some people also call it Mary thistle and holy thistle.

People have traditionally used milk thistle for liver and gallbladder issues and to increase breast milk production. Experts believe silymarin is the main active ingredient of the herb. Silymarin is an antioxidant compound taken from milk thistle seeds. It’s unclear what benefits, if any, it may have in the body, but it’s sometimes used as a natural treatment for things including cirrhosis, jaundice, viral hepatitis, and gallbladder disorders.

Some claim milk thistle may also:

There’s conflicting research on the benefits of milk thistle for liver health. It may have protective effects on the liver, preventing damage. There’s some evidence that milk thistle can treat cirrhosis and chronic hepatitis, which can be caused by alcohol abuse, autoimmune disease, or viruses. But experts say that the evidence isn’t clear.

Some studies also show milk thistle may help people whose liver is damaged by industrial toxins, such as toluene and xylene.

There is not enough scientific data to say whether milk thistle can help liver problems. Learn the facts about milk thistle's potential effects on the liver.

Does milk thistle help with fatty liver?

Research suggests that milk thistle can help treat fatty liver disease, says Sue-Ellen Anderson-Haynes, MS, RDN, CDCES, spokesperson for the Academy of Nutrition and Dietetics and owner of 360Girls&Women B.E.A.T Gestational Diabetes.

One study found that when patients with nonalcoholic fatty liver disease took milk thistle powder for eight weeks, they showed a major improvement in ultrasound fatty liver grading and liver enzymes, which are two key health indicators for fatty liver disease. Another showed that when patients used milk thistle in their treatment for nonalcoholic fatty liver disease, they saw a decline in GGT enzyme activity, which is connected to liver damage.

Medical research suggests that milk thistle, combined with traditional treatment, can improve diabetes. Studies have shown a drop in blood sugar levels and an improvement in cholesterol in people with type 2 diabetes.

Researchers also have found that milk thistle improves insulin resistance, a key part of type 2 diabetes.

Talk to your doctor before taking any supplements because they might interfere with your medication. Learn more about natural remedies for type 2 diabetes.

By lowering LDL “bad” cholesterol levels, milk thistle may lower the chances of getting heart disease. But studies on heart benefits have only been done in people with diabetes. People with diabetes often have high cholesterol. It’s unclear if milk thistle has the same effects in people without diabetes.

Milk thistle can also be taken with cholesterol-lowering medications, such as statins. It can help prevent the levels of liver enzymes from going up, which can be a side effect of the medication. Find out more on the side effects of statins.

The amount of milk thistle needed to see health benefits isn't confirmed for any condition it may be used to treat. The quality of and active ingredients in supplements may vary widely among manufacturers. This makes it very hard to set a standard dose. Ask your doctor for advice on taking milk thistle and the proper amount.

People sometimes eat the stem and leaves of milk thistle in salads. There are no other food sources of this herb.

Taking milk thistle carries certain risks, such as:

Allergic reactions. Milk thistle can trigger allergic reactions. People who are allergic to artichokes, kiwi, ragweed, daisies, marigolds, and chrysanthemums are at higher risk. People who have diabetes or endometriosis should check with a doctor before using milk thistle. While milk thistle has been traditionally used by pregnant and breastfeeding women, its safety is unknown. If you’re pregnant or breastfeeding, check with your doctor before using milk thistle. Milk thistle is not recommended for children.

Estrogen levels. Milk thistle might also affect estrogen levels. You should talk with your doctor about using milk thistle if you have breast cancer, uterine cancer, endometriosis, ovarian cancer, or uterine fibroids.

Interactions. If you take any medicines regularly, talk to your doctor before you start using milk thistle. It could interact with many drugs, including some that treat high cholesterol, infections, insomnia, and blood pressure. Milk thistle may lower blood sugar, so people with diabetes should check with their doctor before taking the herb as it may make their blood sugar fall too low. Other possible drug interactions include medications that treat osteoporosis, blood clotting disorders, hepatitis C, and certain immunosuppressants. 

Does milk thistle have side effects?

Milk thistle seems to have few side effects, even when taken for several years. 

Some people experience nausea, diarrhea, itching, headaches, gas, and bloating. It can increase liver enzymes and bilirubin, which is a substance that gets released when newer red blood cells replace your older ones. Most people don’t experience symptoms from these increases.

It may be problematic for people who are allergic to related plants such as chrysanthemum, marigold, and daisy. 

 “People with an allergy to the aster family, which includes common thistle, kiwi, and artichokes, should avoid milk thistle,” Anderson-Haynes says. 

Can you take milk thistle while breastfeeding?

“Some people take milk thistle or use products with it to help boost breast milk production,” says Anderson-Haynes, adding that there isn't enough evidence about the safety of milk thistle while breastfeeding.

“Breastfeeding mothers have reported nausea, weight gain, and dry mouth with its consumption,” she says.

 

Milk thistle (silymarin) is a flowering herb related to the daisy and ragweed family. People have traditionally used milk thistle for problems with the liver and gallbladder and to increase breast milk production. There’s limited research available about its benefits, but some people use it to treat liver issues,  diabetes, and indigestion. It’s generally considered safe, though it does come with some risks, including allergic reactions. You should talk with your doctor before taking milk thistle. 

What is the best time to take milk thistle?

“It may be best to take milk thistle right before a meal or after a meal to help improve its digestion and absorption,” says Anderson-Haynes.

Is milk thistle good for kidneys?

Milk thistle may help improve kidney health for those with diabetic kidney disease, says Anderson-Haynes, but more research is needed to confirm whether milk thistle is good for the kidneys.

Does milk thistle affect testosterone?

Because milk thistle is a plant estrogen (phytoestrogen), it can help regulate hormone levels, including estrogen and testosterone, says Anderson-Haynes. A review of research studies also suggests that it can raise the levels of testosterone.

What does milk thistle do for women’s health?

If milk thistle can improve liver health, then it can also lead to health benefits for women, says Anderson-Haynes. 

“The liver works to break down and excrete hormones, so a healthy liver is a gold standard in balancing hormones,” she says.