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Does Milk Thistle Have Contraindications?

Known as a safe and effective herb that supports liver health, find out why milk thistle has some concerned about its ability to cause harm.

An herb used for centuries to support the liver’s health, milk thistle is the most reputable and widely used natural approach for preventing liver damage. Although there have been hundreds of studies demonstrating milk thistle’s value to liver health, the evidence is not bulletproof. As is the case with any powerful substance that hasn’t endured the rigorous testing typical of the pharmaceutical industry, there are concerns that milk thistle could be harmful or interfere with other medicines. Especially for those who currently have chronic liver disease and want to supplement with milk thistle to support their liver, it is important to be aware of the potential problems associated with this herb.

About Milk Thistle
A plant native to Europe, milk thistle has a long history as a folk remedy for liver and gallbladder disorders. Found in the seeds of the milk thistle plant, this herb’s active constituent is silymarin. In addition to its status as a potent antioxidant and anti-carcinogenic, clinical studies and reports have found silymarin may help the liver in the following ways:

•    Protects Liver Cells from Damage – Because supplementing with milk thistle is associated with lower enzyme levels of AST (an enzyme that indicates liver damage), scientists believe that this herb protects the liver from damage.

•    Helps Regenerate Liver Cells – Because milk thistle stimulates vital protein synthesis through the enzyme RNA polymerase I, it is believed to be responsible for helping the liver regenerate.

•    Reduces Iron Stored in the Liver – Excess iron might exacerbate liver injury in those with chronic liver disease. Since supplementing with milk thistle appears to lower iron levels, this is another reason why it helps support the liver.

Silymarin is categorized as one of the safest herbs used today. However, those in healthcare know that there are relatively few substances that are 100 percent harmless.

Milk Thistle Concerns
As with any consumable that exerts a strong effect on the body, there are several caveats to be aware of when supplementing with silymarin:

•    Loose Stool – Despite being virtually devoid of side effects, milk thistle’s stimulation of liver and gallbladder activity can have a mild laxative effect in sensitive individuals. If this is the case, experts suggest backing off on the dosage until normal bowel movements are restored.

•    Birth Control – Milk thistle may be capable of reducing the effectiveness of oral contraceptives. One constituent of milk thistle may inhibit an enzyme called beta-glucuronidase, which is involved in the activity of oral contraceptives. Thus, women on oral contraceptives who take milk thistle supplements may want to include a barrier method into their pregnancy prevention plans.

•    Liver Enzyme Inhibition – Certain medications metabolized through the hepatic cytochrome P-450 (especially the enzyme CYP3A4) may be affected by milk thistle. Studies suggesting milk thistle interferes with some drugs have delivered inconsistent results. However, University of Pittsburgh researchers published their findings in 2000 that silymarin inhibits cytochrome P-450. Their finding implies that drugs metabolized by these enzymes remain in the blood longer with milk thistle than they otherwise might.

This lone study is the basis for most of the concern about drug interactions with silymarin. Although many practitioners believe otherwise, some suspect that the following medications may stay in the blood longer in those who also use milk thistle:

•    Methadone

•    Heart drugs – Tambocor (flecainide), Rythmol (propafenone)

•    Antibiotics – Erythromycin, Rifampin

•    Anti-seizure drugs – Carbamazepine (Tegretol)

•    Antidepressants – St. John’s wort, Zyban/Wellbutrin (bupropion), Paxil (paroxetine), Prozac (fluoxetine), Luvox (fluvoxetine) Serzone (nefazodone), Zoloft (sertraline), Effexor (venlafaxine)

•    Antihistamines – Hismanal (astemizole), Seldane (terfenadine)

•    Antifungals – Itraconazole (Sporanox), Ketoconazole (Nizoral)

•    Gastrointestinal motility agents – Prepulsid (Cisapride)

•    Ergot drugs – Ergonovine, Ergomar (ergotamine)

•    Anti-psychotics – Clozaril (clozapine), Orap (pimozide)

•    Sedatives/sleeping pills – Ambien (zolpidem), Halcion (triazolam), Versed (midazolam)

•    HIV medications – Indinavir (Crixivan)

•    Lipid-lowering drugs (statins) – Lescol (fluvastatin), Mevacor (lovastatin), Pravachol (pravastatin) and Zocor (simvastatin), Baycol (cerivastatin)

•    Transplant drugs – cyclosporine (Neoral, Sandimmune), ProGraf (tacrolimus)

Nonetheless, those on any of these (or another drug metabolized via hepatic cytochrome P-450) are wise to discuss their silymarin supplementation plans with their physician. Many physicians recognize that the evidence suggesting milk thistle interferes with certain medications is tenuous, and that there are great benefits of milk thistle for someone with chronic liver disease. To account for the possibility of interference with cytochrome P-450, physicians often advise periodic blood tests to determine drug levels instead of skipping silymarin.

When a substance is potent enough to have real benefits to the human body, it may harbor the potential to do harm under just the right conditions. Despite its stellar safety profile, milk thistle is no exception.

Currently, there is much more evidence favoring milk thistle’s aid to the liver than there is implicating milk thistle in causing harm. Luckily, silymarin’s purported drawbacks – loose stool and interference with certain medications – are rare and can be simply addressed.

References:

http://altmedicine.about.com/cs/herbsvitaminsad/a/Milk_Thistle.htm, Milk Thistle, Retrieved February 4, 2011, About.com, 2011.

http://www.camline.ca/professionalreview/pr_drug_interactions.php?NHPID=51&Section=3&nav=5, Milk Thistle, Retrieved February 4, 2011, CAMline, 2011.

http://www.catie.ca/supple-e.nsf/9f213e0a9cf6ceba85256f5f006dd33c/7b09aa55a412896c85256c6e0070bf60!OpenDocument, Supplement Sheet: Milk Thistle, Retrieved February 2, 2011, Public Health Agency of Canada, 2011.

http://www.hcvadvocate.org/hepatitis/hepC/mthistle.html, A Warning about Milk Thistle and Drug Interactions, Retrieved January 31, 2011, Hepatitis C Support Project, 2011.

http://www.hepatitis-central.com/mt/archives/2009/08/, Four More Key Benefits of Milk Thistle, Nicole Cutler, L.Ac., Retrieved February 4, 2011, Natural Wellness, 2011.

http://www.mskcc.org/mskcc/html/69303.cfm#References, Milk Thistle, Retrieved February 4, 2011, Memorial Sloan-Kettering Cancer Center, 2011.

http://www.ncbi.nlm.nih.gov/pubmed/18249085, Assessment of drug-drug interaction for silymarin, Doehmer J, et al, Retrieved February 4, 2011, Toxicology In Vitro, April 2008.

http://www.skyeherbals.com/materia_medica/milk_thistle.php, Milk Thistle, Retrieved February 4, 2011, Skye Herbals, 2011.

  • Laurie Methven

    Is there any research regarding the use of milk thistle in people who have liver cancer and whether is was of any help?

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