Blessed thistle leaves, stems, and flowers have traditionally been used in "bitter" tonic drinks and in other preparations taken by mouth to enhance appetite and digestion. Blessed thistle may also be included in the unproven anti-cancer herbal remedy Essiac®. This herb has been tested in laboratory studies for its properties against infections, cancer, and inflammation with promising results. However, high-quality trials showing benefits in humans are lacking.
Synonyms
Bitter thistle, Carbenia benedicta, cardin, Cardo Santo, Carduus benedictus, Chardon Benit, Cnici benedicti herba, cnicus, holy thistle, Kardo-benedictenkraut, St. Benedict thistle, salonitenolide, spotted thistle.
Note: Blessed thistle should not be mistaken for milk thistle (Silybum marianus) or other members of the thistle family.
Uses based on tradition or theory
The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Abortifacient, anorexia, appetite stimulant, astringent, bleeding, blood purifier, boils, breast milk stimulant, bubonic plague, cancer, cervical dysplasia, choleretic (bile flow stimulant), colds, contraceptive, diaphoretic (sweat stimulant), diarrhea, digestion enhancement, diuretic, expectorant, fever reducer, gallbladder disease, inflammation, jaundice, liver disorders, malaria, memory improvement, menstrual disorders, menstrual flow stimulant, painful menstruation, rabies, salivation stimulant, skin ulcers, wound healing, yeast infections.
What the Science Says
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Bacterial infections
Laboratory studies report that blessed thistle (and chemicals in blessed thistle such as cnicin and polyacetylene) has activity against several types of bacteria and no effects on some types. Reliable human study is lacking. Further evidence is necessary in this area before a firm conclusion can be drawn.
Indigestion and flatulence (gas)
Blessed thistle is traditionally believed to stimulate stomach acid secretion and has been used as a treatment for indigestion or gas. However, there is limited scientific study in these areas. Additional research is needed before a firm conclusion can be reached.
Viral infections
Laboratory studies report no activity of blessed thistle against herpes viruses, influenza, or poliovirus. Effects of blessed thistle (or chemicals in blessed thistle called lignans) against HIV are not clear. Human research of blessed thistle as a treatment for viral infections is lacking.
Side Effects and Warnings
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Blessed thistle is generally considered to be safe when used by mouth in recommended doses for short periods of time, with few reported side effects. Direct contact with blessed thistle can cause skin and eye irritation.
Blessed thistle taken in high doses may cause stomach irritation and vomiting. Blessed thistle is traditionally believed to increase stomach acid secretion and may be inadvisable in patients with stomach ulcers, reflux disease (heartburn), hiatal hernia, or Barrett's esophagus.
Blessed thistle contains tannins. Long-term ingestion of plants containing tannins may cause gastrointestinal upset, liver disease, kidney toxicity, or increased risk of developing esophageal or nasal cancer. The effects in humans of blessed thistle tannins are not known.
Laboratory studies suggest that blessed thistle may increase the risk of bleeding, although effects in humans are not known. Caution is advised in patients with bleeding disorders or taking agents that may increase the risk of bleeding. Dosing adjustments may be necessary.
Many tinctures contain high levels of alcohol and should be avoided when driving or operating heavy machinery.
Allergies
Allergic reactions to blessed thistle including rash may occur, as well as cross-sensitivity to mugwort and echinacea. Cross-reactivity may also occur with bitter weed, blanket flower, chrysanthemum, coltsfoot, daisy, dandelion, dwarf sunflower, goldenrod, marigold, prairie sage, ragweed, and other plants in the Asteraceae/Compositae family.
Pregnancy and Breastfeeding
Blessed thistle has been used traditionally to stimulate menstruation and abortion, and therefore should be avoided during pregnancy. Although blessed thistle has been used historically to stimulate breast milk flow, it is not recommended during breastfeeding due to limited safety information. Reliable research is lacking in these areas.
Many tinctures contain high levels of alcohol and should be avoided during pregnancy.
Interactions
Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.
Interactions with Drugs
Traditionally, blessed thistle is believed to stimulate stomach acid secretion and it may reduce the effectiveness of drugs such as cimetidine, famotidine, nizatidine, or ranitidine.
Based on laboratory studies, blessed thistle may increase the risk of bleeding when taken with drugs that also increase the risk of bleeding (although effects in humans are not known). Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin or heparin, anti-platelet drugs such as clopidogrel, and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen.
Many tinctures contain high levels of alcohol and may cause nausea or vomiting when taken with metronidazole or disulfiram.
Interactions with Herbs and Dietary Supplements
Based on laboratory studies, blessed thistle may increase the risk of bleeding when taken with herbs or supplements that are believed to increase the risk of bleeding (although effects in humans are not known). Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this may not be proven in most cases.
The FDA does not have the authority to test or approve the safety of herbal products before they are available for your consumption. Since the FDA does not regulate blessed thistle products, there is no guarantee of the strength, purity or safety of blessed thistle products; so effects may vary.
Just because an herbal product is labeled "natural" does not mean it is safe. Herbal supplements and remedies may have harmful effects and can interact with prescription and over-the-counter medications to cause severe side effects and complications.
Read product labels. Speak with your doctor before using any herbal remedy or supplement. Tell your doctor about any herbal remedies you already use and about any complementary and alternative practices you use. Give him/her a full picture of what you do to manage your health. This will help ensure coordinated and safe care. Call your doctor if you experience side effects.
The content of this posting comes from the National Institutes of Health.
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Deborah White, MD, MBA
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