Are There Any Side Effects to Taking Milk Thistle?

People have been using this Mediterranean herb for more than 2,000 years for the protection and healing of the liver, for diabetes control and as an antidote for mushroom poisoning. Milk thistle has been standardized and is available commercially in capsules and extracts. Although there is some scientific evidence to support claims of its benefits, it’s important to be aware of possible side effects and to work with your physician on your treatment.


The primary active ingredient in milk thistle is silybin, and this is what you’ll find in most commercial products. Although milk thistle has been used for thousands of years as a liver treatment, it has made headlines as a treatment for hepatitis and liver disease due to alcoholism. According to an article from the University of Maryland Medical Center, limited studies support some evidence for improvement in liver function in hepatitis but not for cirrhosis due to alcoholism. European studies seem to support using milk thistle to protect the liver from damage. Studies have been conducted for use of silybin in cancer treatment, but the results are inconclusive.


According to the National Institutes of Health, stomach upset can occur when using milk thistle. There have been anecdotal reports of gastronomic distress including bloating, gas and diarrhea. Although these side effects are usually not harmful, they can be uncomfortable and should be treated. Diarrhea should always be taken seriously because it can cause dehydration.

Allergic Reaction

People who are allergic to composites such as ragweed and daisies may have an allergic reaction to silybin in milk thistle. If you get a rash from a composite plant, talk to your doctor about using milk thistle supplements. There also have been reports of anaphalixis, so use milk thistle with caution.


People with diabetes should not take milk thistle without letting their physicians know. According to the National Institutes of Health, there is evidence that the substance can effect blood sugar levels, so careful monitoring and adjustment of the treatment is imperative.

Who Shouldn’t Take Milk Thistle?

Certain groups of people shouldn’t take milk thistle because there hasn’t been enough data collected to guarantee safety. Children and pregnant or nursing women especially are at risk for negative side effects. If you suspect you may have hepatitis or liver problems, see a doctor before you start any type of herb or supplement regimen. Failing to work with a qualified physician could be a fatal mistake.

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