Blessed Thistle (Cnicus Benedictus L.) : Safety and Interactions

by MedlinePlus

(Page 2 of 2)

Safety

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.

Allergies

Allergic reactions to blessed thistle (including contact dermatitis) may occur, as well as cross-reactivity 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, or other plants in the Asteraceae/Compositae family.

Side Effects and Warnings

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 irritation (contact dermatitis) or irritation of the eyes.

Anecdotally, blessed thistle taken in high doses (for example, greater than 5 grams per cup of tea) 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 approximately 8% tannins. Long-term ingestion of plants containing greater than 10% 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.

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. There is no reliable research available 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 may reduce the effectiveness of drugs such as cimetidine (Tagamet®), famotidine (Pepcid®), nizatidine (Axid®), or ranitidine (Zantac®).

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 (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

Many tinctures contain high levels of alcohol, and may cause nausea or vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse®).

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. Some examples include: alfalfa, American ginseng, angelica, anise, Arnica montana , asafetida, aspen bark, bilberry, birch, black cohosh, bladderwrack, bogbean, boldo, borage seed oil, bromelain, capsicum, cat's claw, celery, chamomile, chaparral, clove, coleus, cordyceps, danshen, devil's claw, dong quai, EPA (eicosapentaenoic acid, found in deep-sea fish oils), evening primrose oil, fenugreek, feverfew, fish oil, flaxseed/flax powder (not flaxseed oil), ginger, grapefruit juice, grapeseed, green tea, guggul, gymnestra, horse chestnut, horseradish, licorice root, lovage root, male fern, meadowsweet, nordihydroguairetic acid (NDGA), onion, papain, Panax ginseng, parsley, passionflower, poplar, prickly Ash, propolis, quassia, red clover, reishi, Siberian ginseng, sweet clover, rue, sweet birch, sweet clover, turmeric , vitamin E, white willow, wild carrot, wild lettuce, willow, wintergreen, and yucca.

About the Author

medlineplus.gov
MedlinePlus will direct you to information to help answer health questions. MedlinePlus brings together authoritative information from NLM, the National Institutes of Health (NIH), and other government agencies and health-related organizations. MedlinePlus also has extensive information about drugs, an illustrated medical encyclopedia, interactive patient tutorials, and latest health news.