Blessed thistle, an herb used to treat indigestion, viral infections, diarrhea, bacterial infections and low breast milk supply, is generally safe for most healthy adults. Side effects of blessed thistle are uncommon and generally mild, but it is important to be aware of these potential complications. If you develop any severe or persistent discomforts related to blessed thistle use, stop using the herb and consult your health care provider.
The following side effects of blessed thistle may occur, particularly if you have certain medical conditions.
Compounds in blessed thistle can irritate the lining of your digestive tract, leading to mild to moderate inflammation in your stomach and intestines. This can create a burning sensation, abdominal pain, diarrhea and, very rarely, blood in the stool. Because of this side effect, blessed thistle should be avoided by people with inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis.
Some people experience nausea or vomiting as a side effect of blessed thistle. Blessed thistle’s capacity to induce vomiting may relate to its stomach-irritating properties. If you vomit after using blessed thistle, stop using the herb. Consult your health care provider if the problem is persistent or severe.
As a member of the ragweed family, which also includes other medicinal herbs such as milk thistle, chamomile, echinacea and valerian, blessed thistle may trigger allergic reactions in susceptible individuals. If you are allergic to another member of te ragweed family, use blessed thistle with caution. Very large doses of blessed thistle might cause hives, wheezing and severe diarrhea in people who are allergic to it.
Do not use blessed thistle if you are pregnant. Side effects of blessed thistle during pregnancy might include vaginal bleeding, miscarriage, preterm labor and birth defects in the developing fetus. However, blessed thistle can be used safely by nursing mothers for brief periods of time; it may help to increase breast milk supply.
Visit the National Institutes of Health for more information about blessed thistle side effects.