Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066





(for veterinary information only)



Numerous herbal brands are available (usually as seed extract)

Veterinary brands include: Marin (which combines silymarin with vitamin E and phosphatidyl choline) and Denamarin (which combines silymarin with SAMe)



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, which is also called “silybinin” and is considered the most powerful of them all. 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, most scientific information available concerns human use. The biological mechanism of action is yet unknown but several theories exist:

Milk Thistle (Silybum marianum)

Milk Thistle (Silybum marianum)

  • Silymarin may control cell membrane permeability which means that silymarin may control what substances actually enter the interior of a cell.
  • Silymarin may inhibit inflammatory biochemical pathways.
  • 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.



In human patients with cirrhotic livers, with alcohol-induced hepatitis, and with liver disease from Hepatitis C, silymarin has been shown to improve symptoms, laboratory tests, and survival. Silymarin has not been investigated formally for all liver diseases but it is a very safe substance and should not cause problems if used in a liver situation where its benefit is unproven. In dogs and cats, silymarin has been shown to be helpful in cases of Aminita mushroom toxicity and was protective after carbon tetrachloride administration (both are situations being toxic liver diseases).

Phosphatidyl choline is added to some oral preparations of silymarin as it enhances silymarin absorption into the body from the GI tract.



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.



Please keep in mind 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. Using a product from a reputable manufacturer is especially important.

Silymarin combined with cisapride, an intestinal motility enhancer, can lead to heart rhythm disturbances.



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.

Milk thistle products may be given with or without food, however, SAMe which is often combined with silymarin, is best given on an empty stomach.



Because herbal medications are not held to the same purity and efficacy standards
as other medications, there may tremendous variation in strength
between brands or even between batches of the same brand.
We recommend checking with your veterinarian about what brand he or she feels is reliable.


 Page last updated 3/24/2022