In high dosage it may cause hypothyroidism and liver dysfunction10. Silymarin (flavonolignan obtained from seeds of milk thistle) contain a number of different active principles like flavonoids having potential prophylactic and therapeutic activity against many liver diseases11,12.
There is also concern that milk thistle might affect estrogen levels. If you have breast cancer, uterine cancer, ovarian cancer, endometriosis or uterine fibroids, consider avoiding milk thistle.
Some Supplements Can Affect Thyroid Medication
According to the Mayo Clinic, supplements such as calcium, iron, multivitamins containing iron, and antacids containing magnesium or aluminum can potentially have interactions with thyroid medications.
Milk thistle doesn't have a direct effect on thyroid health. However, this doesn't mean that people with thyroid and autoimmune thyroid conditions can't benefit from taking this herb.
Milk thistle should not be used by pregnant or breastfeeding women. People with a history of hormone-related cancers, including breast, uterine, and prostate cancer, should not take milk thistle. DO NOT take milk thistle if you are allergic to ragweed, chrysanthemums, marigolds, chamomile, yarrow, or daisies.
Milk thistle is generally considered safe for most people at dosages up to 420 mg 3 times a day. However, it may cause allergic reactions, such as itching, headaches, and joint pain, or gastrointestinal symptoms like nausea or diarrhea.
Vitamins and supplements
“You should also avoid any drugs or supplements that contain iron, calcium, or magnesium for at least four hours after taking your thyroid medications,” says Dr. Jaiswal. That also includes multivitamins that contain these minerals.
Biotin is a common component of multivitamin preparations and at high doses it has been reported to cause interference in immunoassays resulting in abnormal thyroid function tests [2].
Specifically, antacids, calcium, cholesterol drugs, and iron supplements can each interfere with the way the thyroid hormone is absorbed. So, you should take these particular drugs four hours before or after taking your thyroid medication, according to the U.S. National Library of Medicine.
A huge proportion of the sodium we consume comes from processed foods and it is recommended that those with hypothyroidism should avoid excess sodium. Having an underactive thyroid increases your risk of developing high blood pressure and eating too much sodium can increase this risk further!
No interactions were found between levothyroxine and milk thistle.
Milk thistle might decrease the effects of medications providing estrogen by blocking how estrogen works in the body.
Milk thistle has been shown to have estrogenic-mimicking effects, about on par with common soy isoflavones, making them a theoretically poor choice for people with breast cancer.
Bugleweed (Lycopus virginicus, Lycopus europaeus) and lemon balm (Melissa officinalis) may interfere with the action of thyroid hormones. Check with your doctor before taking these herbs with thyroid hormones. The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
How magnesium affects the thyroid. We need magnesium to convert the inactive thyroid hormone T4 into the active thyroid hormone T3. Without this conversion, cells do not receive the more potent form of thyroid hormone. Therefore, when magnesium levels are low, our thyroid is not able to function correctly.
Natural remedies for hyperthyroidism include a whole foods-based diet free of processed foods, avoiding common food allergens and iodine sources, regular exercise and more. If you opt to take medication for hyperthyroidism, it's important that you are aware of the side effects.
Early research shows that taking milk thistle extract by mouth for up to one year, or taking a product containing the milk thistle constituent silybin plus phosphatidylcholine by mouth for 1 week, improves liver function tests.
Supports liver health
The active ingredient in milk thistle, silymarin, acts as an antioxidant by reducing free radical production. Scientists think this creates a detoxifying effect, which is why milk thistle may be beneficial for liver problems.
Milk thistle is considered safe in dosages of 420 mg/day orally in divided doses for up to 41 months.