Consider Milk Thistle for:
  • Chronic Liver disease
  • Acute Hepatitis
  • Viral Hepatitis
  • Liver poisonings including aflatoxins
  • When using drugs that can injure the liver (NSAIDS, Phenobarbitol)
  • Preventative in animals with history of liver disease
  • Early stages of liver enzyme elevation
  • Lead and Zinc poisoning
  • Inflammatory cardiac (Heart) diseases
  • Kidney disease
  • Immune modulation
  • Antioxidation
  • Delays the onset and severity of diabetes
  • Effective for pancreatitis
  • Liver cirrhosis
  • Fatty Liver

Silymarin is not recommended for humans during pregnancy. It is probably a good idea not to use milk thistle products in pregnant dogs until more information becomes available.


I would like to tell you about a wonderful herb and a must for every pet owner's natural medicine chest. Milk thistle, known in Latin as Silybum marianum, is one of the most effective herbs for detoxifying and regenerating the liver. I have used this herb in virtually any type of liver problem. It has saved many pets from what appeared to be a fatal condition. The liver is responsible for breaking down and eliminating most toxic substances. These include drugs, preservatives in food, artificial flavoring and coloring agents, flea sprays, dips and shampoos, environmental chemicals, chemicals found in tap water, household cleansers, air pollution, tobacco smoke and poisonous plants. Hundreds of scientific studies have demonstrated that milk thistle can protect the liver from potent toxins such as poisonous mushrooms, heavy metals and alcohol. 

How does it work? When the constituents of milk thistle are absorbed, they selectively accumulate in the liver. The herb has several mechanisms of action.

  • It stimulates protein synthesis, which contributes to re-generation and replacement of liver cells.

  • It helps protect the liver against poisoning by blocking the absorption of toxins into liver cells.

  • It inhibits the formation of inflammatory substances that contribute to liver degeneration. 

  • It helps the liver break down toxins.

Milk Thistle for DogsMilk thistle is a potent anti-oxidant (more potent than Vitamins C and E). This means it can counteract free radical damage that can cause degenerative diseases including cancer.
It increases intracellular levels of glutathione, a substance necessary for detoxicating reactions. Milk thistle has a long history of use and no significant toxicity has been seen. 
Clinical studies in humans have confirmed milk thistle's benefits. Trials in more than 2,000 patients showed benefits in alcohol and chemical induced fatty liver, cirrhosis, chronic hepatitis, bile duct inflammation and non specific changes in liver tissue. Elevated liver enzymes (blood tests for liver function) also improve with milk thistle therapy. Silymarin may also help prevent or treat gallstones by increasing the solubility of the bile. The best-known active compound in milk thistle is silybin. It is important to remember that there are many other naturally occurring ingredients that are vital for optimum activity. Therefore, use the whole herb or a high quality extract. 

Many drugs used today have significant liver toxicity. If your pet has been medicated with antibiotics, cortisone, chemotherapy, anti-seizure medications, heartworm preventive / treatment, anti-inflammatory, etc. or has had other liver problems, you should consider a course of milk thistle. Of course, it is also important to reduce your pet's exposure to liver toxic substances. Most drugs can be eliminated under the supervision of a holistic veterinarian through the use of natural alternatives. Toxic additives in the food and water can be reduced significantly by feeding balanced, home-prepared foods and purified water. A low toxicity flea control program can be instituted until the pet is healthy enough to no longer require it. (That's right, healthy pets don't have significant flea problems.) For household cleaning, vinegar and hydrogen peroxide are two safe alternatives. 

When shopping for milk thistle, I prefer a standardized (70 or 80% silybin) product. A typical adult human dose is 100 - 150 mg. of silybin, which is approximately 200 mg. dry herb three times daily, or the equivalent in a liquid. For pets, simply use their body weight as a percentage of the human dose. For example, a 30-pound dog would get 30% of a human dose and a 10-pound cat would get 10%. Most products purchased at health food stores have the recommended human dose on the label. Give it for 2-3 months. Medicinal herbs should not be used continuously for extended periods. I suggest 5 days on then 2 days off for 6 weeks. Skip 1 week and begin again. It could be used one week each month as a little extra protection in otherwise healthy pets. 

by Russell Swift DVM 

© Copyright June, 1999 - 2005
Russell Swift is a 1985 graduate of the University of Florida College of Veterinary Medicine. He has completed the Homeopathic Master Clinician program and currently has a holistic house call veterinarian practice in the South Florida area. He is also a consultant for several companies in the development of new nutritional supplements for pets. Dr. Russell Swift can be reached at 954-720-1624. 

 Recommended Dosage

Dog's size

% of adult human dose
5 lbs 10%
5-10 lbs 15%
11-20 lbs 20%
21-40 lbs 30%
41-70 lbs 50%
71-100 lbs 75%
100 lbs 100%
Go here to convert weights


Milk thistle is a flower, more specifically a member of the aster family. Its seeds and roots have been used for an assortment of medical purposes for thousands of years. Three biochemicals of interest have been isolated from the milk thistle: silychristine, silydianin, and silybin. The mixture of these three substances is called Silymarin. Silymarin has been traditionally used in the treatment of liver disease and, while it has recently been advocated for use in pets, all scientific information available concerns human use. The biological mechanism of action is yet unknown but several theories exist:

  • Silymarin may control cell membrane permeability, which means that silymarin may control what substances enter the interior of a cell.

  • Silymarin may inhibit chemical pathways leading to inflammatory biochemicals.

  • Silymarin may have free radical scavenging properties, which means that it may absorb harmful reactive atoms that could damage other molecules.

  • Silymarin may increase protein production by liver cells.

  • Silymarin may stabilize mast cells (cells containing inflammatory granules).

  • Silymarin in higher doses increases the flow of bile.

How This Medication Is Used
The most scientific information concerning the use of Silymarin regards Amanita mushroom poisoning. Silymarin prevents uptake of the poison into the cells of the liver and thus prevent the lethal liver damage associated with this type of mushroom poisoning.

Silymarin is regularly used for an assortment of liver diseases including cirrhosis and viral hepatitis in humans. The only actual studies conducted in dogs have concerned mushroom poisoning as above and other uses in pet species are inferred from human use. Milk thistle extracts appear to be safe to use; however, their benefit is not well defined scientifically.

Side Effects
At doses greater than 1.5 grams per day, the increased bile flow side effect may cause diarrhea. Side effects are very rare but the following has been reported for humans: upset stomach, headache, joint pain, weakness.

Interactions with Other Drugs
While there are no known drug interactions, it is important to remember that herbal medications are not held to the same standards of efficacy and safety that other drugs are. Impurities in processing may include less innocuous plant biochemicals.

Concerns And Cautions
Silymarin is not recommended for humans during pregnancy. It is probably a good idea not to use milk thistle products in pregnant dogs until more information becomes available.

Milk thistle products should be stored at room temperature.

Because herbal medications are not held to the same purity and efficacy standards as other medications, there may be tremendous variation in strength between brands or even between batches of the same brand.

By Wendy C. Brooks, DVM, DipABVP 
Educational Director, 
Web Page

  Milk Thistle (Silybum marianum )

Constituents: flavolignans, silymarin (silybin, silydianin, isobilybin), bitter, amines, tannin, polyactylenes.

Energy: pungent, warm, bitter, dry.

Western uses: Stimulates digestion, reduces liver congestion, promotes bile flow, vitalizes blood, promotes tissue repair, reduces hepatotoxicity (autotoxicity and ingested toxins)

Veterinary Examples: All animals with any form of hepatotoxicity or hepatic damage may benefit from Milk Thistle. Patients on hepatotoxic drugs, those with hepatitis, liver cirrhosis, liver degeneration, and functional biliary obstruction can be helped by this powerful herb. What do you currently know as medical options for pathological changes in liver tissue? Milk thistle may also be used as an adjunct detoxicant in any condition that is currently treated with toxic drugs. For example, if heartworms are a problem in your region, the USDA approved monthly heartworm preventatives (e.g. HeartgardTM, InterceptorTM) may be given while using milk thistle to protect the liver. Milk thistle also may be used as part of a regular detoxification program due to our inhabiting, even on the best days, a toxic planet. Lastly, during the healing and "clean-up" phase of tissue repair, the liver has extra work to do and can be benefited by Milk Thistle as a dietary addition.


Milk Thistle is a unique herb which contains a natural compound called silymarin. Silymarin nourishes the liver like no other nutrient currently known. The liver acts as the body's filter constantly cleansing to protect you from toxins. Over time, these toxins can accumulate in the liver. Milk Thistle's potent antioxidant properties and rejuvenating actions help keep the liver strong & healthy. 


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