Side Effects of Milk Thistle

Milk thistle has been used for more than 2,000 years for its medicinal properties. In modern integrative medicine, milk thistle may be used as a complementary treatment for cirrhosis, viral hepatitis and gallbladder disorders.

In general, milk thistle is well-tolerated and associated with few side effects or drug interactions. Serious adverse events are rare and generally attributed to undiagnosed allergies. However, people who are interested in taking the herb should be aware of the possible milk thistle side effects and drug interactions.

Gastrointestinal Side Effects

Rarely, milk thistle can cause upset stomach and other digestive complaints. Among the gastrointestinal side effects of milk thistle are:

Reflux
Heartburn
Nausea
Loose stools
Cramping
Flatulence
Bloating
Belching

Hormonal Effects

Like many herbs, milk thistle contains trace amounts of compounds that may interfere with levels of estrogen in the body. While there is no conclusive evidence that milk thistle affects hormone levels, caution is advised. Milk thistle side effects could theoretically worsen:

Impotence
Prostate cancer
Pregnancy complications
Endometriosis
Uterine fibroids
Breast cancer
Ovarian cancer

Drug Interactions

Milk thistle can interact with prescription and over-the-counter drugs, including other medicinal herbs. Few studies have determined milk thistle's safety when it is combined with prescription treatments. Talk to your doctor before taking milk thistle if you are taking any prescription drug, especially:

Antipsychotics (Haloperidol, Chlorpromazine, Fluphenazine, Promethazine)
Phenytoin (Dilantin)
Fexofenadine (Allegra)
Statins (Mevacor, Altocor)
Anxiolytics (Ativan, Xanax, Valium)
Anticoagulants (Plavix, Coumadin)

Allergic Reactions

Very rarely, people have developed severe allergic reactions to milk thistle. In theory, these reactions may be more common in people who have allergies to other members of the same botanical family, such as ragweed and echinacea. Symptoms of a milk thistle allergy include:

Rash
Diarrhea
Vomiting
Wheezing
Dizziness
Collapse
Difficulty breathing

Aches and Pains

Some patients report minor aches and pains as milk thistle side effects. These are only slightly more common than in people taking placebo. Some possible problems include:

Headache
Neck tension
Backache
Abdominal pain
Joint pain
Flu-like tenderness