Milk Thistle: Side Effects & Interactions

Updated November 21, 2016

Many people are looking to nature and to the past to find remedies for their ailments and their symptoms. Milk thistle has been in use for 2,000 years. Pliny the Elder extolled the virtues of the herb back around the time of Christ and so have many others over the millennia. Its primary reputation as a healing herb is for the effect it has on the liver and various ailments of the liver. Milk thistle may be all natural, but it still can have side effects and interactions.


The theory behind the effectiveness of milk thistle in treating liver problems derives from how it is thought to affect the cells in the liver. Herbalists believe that milk thistle strengthens the outer wall of liver cells, shields the cells from damaging free radicals and stimulates the production of new cells in the liver. The chemicals in milk thistle are flavonoids, much like the active compound in garlic, which have been shown to have anti-inflammatory properties. They are also powerful antioxidants.


Studies on the effectiveness of milk thistle on cirrhosis, hepatitis, liver damage from alcohol and cancer are mixed. It has been shown to be an effective emergency antidote to the deathcap mushroom, preventing both death and liver damage if taken shortly after ingestion of the fungus.

Side Effects

Side effects of milk thistle are generally mild, and can include diarrhoea and stomach upset. Touching the plant may cause a rash in some people. Women who are pregnant or nursing should not take milk thistle. Neither should people with a history of hormone-related cancers, such as uterine, breast or prostate cancer.

Drug Ineractions

Many herbs can cause interactions with other herbs, as well as medications. If you are taking milk thistle, make sure your doctor and your pharmacist are aware of this when you are prescribed any medication. Some of the drugs known to react badly to milk thistle are: antipsychotics like phenothiazines and butyrophenones, the seizure medication phenytoin and the anaesthesia drug halothane. Milk thistle interferes with the effectiveness of allergy drugs such as fexofenadine, cholesterol drugs like lovastatin and some cancer drugs. Anti-platelet and anticoagulant drugs such as warfarin and clopidogrel are affected, as are anti-anxiety drugs, including diazepam, alprazolam, and lorazepam.


As you can see, this is a pretty long list of drugs and may not be all inclusive, especially as new drugs are introduced into the marketplace all the time. Because of this, it is important that you let your doctor know about any herbs you are taking, including milk thistle. Many people neglect to tell their health care providers, which causes preventable complications. All natural does not always mean safe, so use the same care with herbs as you would with any drug. Follow instructions and keep on the lookout for any unusual side effects. If you are not getting relief, or are having serious side effects, stop taking milk thistle.

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