Milk thistle may be used by some people to manage endometriosis symptoms, but studies are inconclusive on whether it provides any real benefits.

Although medications such as progestins and oral contraceptives are the first-line treatment for endometriosis, they don’t successfully treat symptoms in about one-third of people with endometriosis.

Therefore, herbal and natural alternatives, such as milk thistle, continue to be investigated for their potential role in the long-term management of endometriosis symptoms.

Milk thistle (Silybum marianum) is a medicinal plant from the Asteraceae family, which also includes daisies and sunflowers. The plant has been used for thousands of years in traditional and herbal medicine systems around the world to treat various ailments, most notably liver diseases.

The fruits and seeds of the plant — which contain silymarin, the active component of milk thistle — are crushed and used alone or in concoctions with other herbs. Silymarin is a group of health-promoting flavonoids that give milk thistle its healthful properties.

Also called St. Mary’s thistle, holy thistle, Christ’s crown, and wild artichoke. Milk thistle is available over the counter as a dietary supplement in the form of capsules or liquid concentrates.

Read on to learn what science has to say about the safety and efficacy of using milk thistle to manage symptoms of endometriosis.

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Here are some ways that milk thistle may help with endometriosis.

Lowers inflammation and pain

Endometriosis is now considered a systemic condition that causes inflammation throughout the body, and not just in the pelvic region.

Silymarin, the main extract of milk thistle and a group of flavonoids, may have beneficial anti-inflammatory properties.

Animal research in mice demonstrated that silibinin, one type of silymarin, reduced the release of inflammatory cytokines that are associated with endometrial lesions.

Likewise, test tube research on gastrointestinal cancer cells showed that silymarin reduced inflammation and may improve symptoms associated with cancer and its therapies.

More research is needed on the effects of silymarin in humans living with endometriosis.

May reduce the growth of endometrial lesions

Milk thistle extracts are shown in animal research to reduce the multiplication of endometrial tissue outside of the uterus, and in turn, stop the growth of endometrial lesions.

While symptoms from endometrial lesions may vary, they can become inflamed and induce severe pain in some people. They may also contribute to a reduction in the quality of life for people living with endometriosis.

Milk thistle is generally considered safe when taken by mouth.

The National Cancer Institute (NCI) has documented that large, clinical trials in humans provide evidence that the silymarin extract of milk thistle is well-tolerated, with minimal and rare side effects seen at doses above 1500 mg per day.

However, other human research showed that silymarin is safe in humans up to 2100 mg per day — taken in 700 mg doses three times per day — for up to 24 weeks.

It’s important to always check with a healthcare professional before starting a new supplement, especially if you take other medications.

In rare cases, people may report the following side effects:

  • diarrhea
  • nausea
  • bloating

Allergic reactions may also be seen in people with allergies to other plants in the Aster family, like daisies.

In addition, milk thistle is available over the counter as dietary supplements, many of which are not regulated by the Food and Drug Administration (FDA).

This means that, for some supplement brands, it’s not guaranteed that the ingredients listed on the label are actually found in specified amounts, which impacts the potential benefits of the product.

Choose supplements that have independent, third-party testing, and always check with your healthcare professional before taking a new supplement.

More well-designed clinical trials in humans are needed to determine the long-term health impacts of milk thistle use in the management of chronic, noncommunicable conditions such as endometriosis.

Does milk thistle increase estrogen?

Milk thistle is considered to be an estrogenic plant, or a plant with estrogen-like properties in the body. However, it’s not clear whether the milk thistle plant itself or high doses of its extracts significantly increase estrogen levels and contribute to the growth of painful endometrial lesions.

Who should not take milk thistle?

Given the lack of human research, some people should be cautious when taking milk thistle:

  • persons with allergies to the Asteraceae plant family
  • pregnant people
  • persons with estrogen-sensitive conditions, such as some types of breast cancers

Endometriosis is a chronic, inflammatory condition marked by the growth of endometrial tissue outside of the uterus.

It’s associated, in some cases, with:

  • endometrial lesions
  • inflammation
  • painful menstrual cycles
  • liver dysfunction
  • infertility

The milk thistle plant contains a group of health-promoting flavonoids called silymarin, that may be effective in managing endometriosis by lowering inflammation, reducing the growth of endometrial lesions, and improving liver function.

However, research is inconclusive and study results vary on the effectiveness of milk thistle for managing endometriosis. Always discuss the benefits and risks with a healthcare professional before beginning any new supplements.