There are a number of known and potential milk thistle side effects that should be considered before taking milk thistle, including some isolated side effects and a few possible negative drug interactions. Some known milk thistle side effects include nausea, diarrhea, indigestion, and loss of appetite. Milk thistle is a plant within the daisy family and gains its name both from the white splotches that appear on the leaves and the white sap contained within the plant. The leaves are often eaten in salads as a replacement for lettuce or spinach, and the seeds can be ground up and used in beverages in place of coffee beans. There are also milk thistle extracts that can be used as dietary supplements, usually intended to combat or prevent liver damage.
While milk thistle side effects include a number of unpleasant intestinal and digestion related issues, it can be used as a natural laxative. Milk thistle is likely safe for most healthy adults, but if any side effects do occur, the person should stop taking it immediately and consult a physician before further use. There is little research regarding possible milk thistle side effects for women who are pregnant or nursing, and it should probably be generally avoided during such times.
Milk thistle side effects have also been shown to include an allergic reaction in people who are allergic to plants of the Asteraceae/Compositae family. These include ragweed, chrysanthemums, and daisies. Anyone with allergies to these plants should avoid consumption of milk thistle without first consulting a physician.
Other milk thistle side effects can come from extracts of the plant acting like estrogen in some people. Anyone with a condition that could be made worse from the effects of increased estrogen, such as certain types of cancer, should avoid these types of extracts. Extracts made from milk thistle seeds, however, have not been found to have these effects. Milk thistle has also been shown to reduce the effectiveness of estrogen hormone treatments. Milk thistle seems to help the body break down estrogen supplements faster, so taking both can reduce the amount of estrogen actually gained from the treatments.
Known milk thistle side effects include interaction with medication used for lowering cholesterol. Milk thistle may change the amount of such medications within a person, which can increase or decrease the effectiveness of the medication. Anyone taking this type of medication should consult his or her physician before taking milk thistle.
Though milk thistle is used to help people who have livers that have been damaged through exposure to toxic chemicals, it should not be taken with drugs that are broken down for the body by the liver. Some medications are broken down by the liver to work effectively in the human body, and research has shown that milk thistle can slow that process, extending the period of effectiveness of the medication in the human body. This can lead to potential overuse of such medication or can increase the period of time in which negative interactions between medications can occur.
