Milk Thistle for Dogs (Silymarin)

Milk thistle is a supplement with powerful antioxidant properties that is used to treat and protect against liver damage. Milk thistle supplements may be especially beneficial for your dog when used with certain types of chemotherapy.

Key Takeaways

  • Milk thistle protects dogs’ liver cells from damage and may protect against side effects from chemotherapy.
  • In general, you should give a dog 20-50mg/kg of milk thistle for liver protection once a day. Follow dosing instructions for products containing milk thistle.
  • Milk thistle is safe for dogs.
  • Milk thistle can reverse liver damage in dogs.
  • You can help to naturally heal your dog’s liver by giving a milk thistle product.

Silymarin for Dogs

Milk thistle is a flowering plant originally native to Europe that is now found throughout the world. Parts of the milk thistle plant have been used in traditional herbal medicine for thousands of years.

Silymarin is a combination of three chemicals isolated from the fruit of the milk thistle plant: silychristine, silydianin, and silybin. Silybin is the most active ingredient of the extract.1

Silymarin and silybin (also known as silibinin) extracts are widely used in human and veterinary medicine. Veterinary brands containing silybin include:2

  • Marin – a combination of silymarin, vitamin E, and phosphatidyl choline (PEP)
  • Denamarin – a combination of silymarin and S-adenosylmethionine (SAMe)
  • Marin and Denamarin are used for management of liver disease. They help to protect liver cells from apoptosis (cell death) and fibrosis (thickening or scarring).3

Evidence for Efficacy

Silymarin is often used in human and veterinary medicine for the treatment of liver disease.

In human patients with alcohol-induced liver damage and liver disease from Hepatitis C, silymarin has been shown in some studies to decrease symptoms, improve laboratory tests, and increase survival time.2

Results from clinical trials in human medicine have been conflicting, and some studies show no clinical benefit for patients with liver disease.4

In veterinary studies, treatment with silymarin appeared to be beneficial to dogs after ingestion of toxins that harm the liver, including Aminita mushrooms and carbon tetrachloride.2

Silymarin supplements also show potential to protect against Alzheimer’s disease in humans. In a study using mice, silymarin helped to decrease the levels of a protein (amyloid-beta) that impairs the function of brain cells and worsens Alzheimer’s symptoms. Mice in the study treated with silymarin also had decreased anxiety symptoms. More research is needed to know if silymarin may be helpful for behavioral changes in older dogs caused by canine cognitive dysfunction.9

Silymarin and Cancer

There is evidence to suggest silymarin may reduce the side effects of cancer treatment. A clinical trial in children with acute lymphoblastic leukemia (ALL) demonstrated silymarin supplements protected liver cells from the side effects of the chemotherapy drugs vincristine and L-asparaginase.5

Milk thistle supplements also had a protective effect on kidney cells in vitro, or in a lab, when the chemotherapy drug cisplatin was used.6

In a human clinical trial, patients undergoing radiation treatment for head and neck cancer who took silymarin supplements had decreased mucositis, or inflammation and pain in the tissues of their mouths (mucositis can also refer to inflammation of the gut when radiation is focused on other parts of the body).7

Topical silymarin gel was used in a study of human breast cancer patients undergoing radiation therapy, and the silymarin product decreased the severity of skin inflammation caused by radiation treatment.8

The effect milk thistle supplements have on cells in the body to produce their protective effects is still being explored. Silybin is an antioxidant and has a protective effect in several body tissues.

Some researchers believe silymarin has an effect on cell membrane permeability, and silymarin may control which substances enter and leave cells. Silymarin may help liver cells to produce more proteins, improving the liver’s overall function. More research is needed to confirm silymarin’s effects on the body.2

Common Uses of Silymarin for Dogs

  • Liver disease
  • Antioxidant
  • Improved tolerance to chemotherapy and radiation treatments

Milk Thistle Dogs Side Effects

Silymarin supplements and the veterinary products Marin and Denamarin are usually well tolerated by dogs.10 As with any oral supplement, monitor for nausea, vomiting, and diarrhea.

Side effects of silymarin supplements reported in humans include headache, itchy skin, nausea, diarrhea, and vomiting. Allergic reactions have been reported, and silymarin products are not recommended for people or animals with a history of allergies to closely related plants including ragweed, daisies, marigolds, and chrysanthemums.11

Can Be Given With

Silymarin supplements can be used safely with chemotherapy, radiation, and surgery.12,13

While milk thistle products are often well tolerated, check with your veterinarian before using silymarin products in combination with other medications and supplements.

When to Not Use Milk Thistle for Dogs

There are some situations where milk thistle is not a good choice or should be used with caution.

  • Silymarin combined with cisapride, a drug that increases intestinal motility, can lead to heart rhythm disturbances.2
  • Silymarin products may affect the enzyme cytochrome P450 2C9 (CYP2C9). The drugs processed by this enzyme include diazepam and warfarin, and silymarin products may impact their levels in the body.11
  • Silymarin supplements might lower blood sugar in people with diabetes.11 Marin and Denamarin appear to be well tolerated by dogs with diabetes, however, talk to your veterinarian about blood glucose monitoring prior to starting silymarin supplements. An accidental overdose of insulin can lead to a medical emergency if left untreated.10
  • Milk thistle supplements may affect estrogen levels, and people with breast cancer, uterine cancer, or ovarian cancer are often encouraged to avoid silymarin products. Silymarin is not recommended for people or dogs during pregnancy.11

Silymarin products that are combined with S-Adenosylmethionine (SAMe), like Denamarin, may have interactions with:14

  • Acetaminophen
  • Amitriptyline
  • Clomipramine
  • Dextromethorphan
  • Diazepam
  • Fluoxetine
  • Mirtazapine
  • Monoamine oxidase (MAO) inhibitors such as selegiline
  • Meperidine
  • Metronidazole
  • Morphine
  • Pentazocine
  • Tramadol
  • Trazodone

Milk Thistle for Dogs Dosage

Milk thistle supplements are available as capsules, tablets, and liquid extracts.15

Phosphatidyl choline (PEP) is added to some oral milk thistle supplements to aid in its bioavailability, or the proportion of the product that is absorbed into the bloodstream.2

Silymarin dosage for liver protection is 20-50 mg per kilogram of body weight per day by mouth. This dose is often given once daily, most milk thistle supplements are labeled with a twice a day dosage.

The suggested dose of the veterinary product Denamarin for the protection of liver cells is 1.2-4mg per kilogram of body weight of silybin (also called silibinin) with 15-38mg per kilogram of body weight of SAMe per day. This dose is often given once per day.

Per the label directions, for optimal absorption Denamarin should be given on an empty stomach at least one hour before a meal. Denamarin is available as a tablet or flavored soft chew.

The suggested dose of the veterinary product Marin for the protection of liver cells is 1.6-3.1 mg per kilogram of body weight per day by mouth. This dose is often given once per day. Marin is available as a flavored soft chew.

What If I Miss a Dose?

Give the next dose as soon as you remember, then wait the recommended time until the next dose. Missing a dose is not likely to have significant effects.

Storage and Handling

Store milk thistle products in a cool, dry place out of direct sunlight, and refer to the product packaging for specific instructions. There is no special handling or personal protective equipment (PPE) required.

Our Take on Milk Thistle for Dogs

Milk thistle supplements can support your dog’s immune system and liver function during cancer treatment. Ask your veterinary team if silymarin would be a good addition to your dog’s treatment plan.

  1. Guerrini A, Tedesco DEA. Use of Milk Thistle in Farm and Companion Animals: A Review. Planta Medica. Published online October 27, 2022. doi:10.1055/a-1969-2440
  2. Paul Pion DVM, Spadafori G. Veterinary Partner. VINcom. Published online August 8, 2017. Accessed January 31, 2023.
  3. Chan DL. Nutritional Management of Hospitalized Small Animals. John Wiley & Sons; 2015. Accessed January 31, 2023.
  4. Milk Thistle. NCCIH.
  5. Ladas EJ, Kroll DJ, Oberlies NH, et al. A randomized, controlled, double-blind, pilot study of milk thistle for the treatment of hepatotoxicity in childhood acute lymphoblastic leukemia (ALL). Cancer. 2010;116(2):506-513. doi:10.1002/cncr.24723
  6. Ninsontia C, Pongjit K, Chaotham C, Chanvorachote P. Silymarin selectively protects human renal cells from cisplatin-induced cell death. Pharm Biol. 2011;49(10):1082-1090. doi:10.3109/13880209.2011.568506
  7. Elyasi S, Hosseini S, Niazi Moghadam MR, Aledavood SA, Karimi G. Effect of Oral Silymarin Administration on Prevention of Radiotherapy Induced Mucositis: A Randomized, Double-Blinded, Placebo-Controlled Clinical Trial. Phytother Res. 2016;30(11):1879-1885. doi:10.1002/ptr.5704
  8. Karbasforooshan H, Hosseini S, Elyasi S, Fani Pakdel A, Karimi G. Topical silymarin administration for prevention of acute radiodermatitis in breast cancer patients: A randomized, double-blind, placebo-controlled clinical trial. Phytother Res. 2019;33(2):379-386. doi:10.1002/ptr.6231
  9. Murata N, Murakami K, Ozawa Y, et al. Silymarin attenuated the amyloid β plaque burden and improved behavioral abnormalities in an Alzheimer’s disease mouse model. Biosci Biotechnol Biochem. 2010;74(11):2299-2306. doi:10.1271/bbb.100524
  10. Liver Health Support For Dogs & Cats – Denamarin®. Accessed February 1, 2023.
  11. Milk thistle. Mayo Clinic. Published 2017.
  12. Delmas D, Xiao J, Vejux A, Aires V. Silymarin and Cancer: A Dual Strategy in Both in Chemoprevention and Chemosensitivity. Molecules. 2020; 25(9):2009.
  13. Ramadan LA, Roushdy HM, Abu Senna GM, Amin NE, El-Deshw OA. Radioprotective effect of silymarin against radiation induced hepatotoxicity. Pharmacological Research. 2002;45(6):447-454. doi:10.1006/phrs.2002.0990
  14. Paul Pion DVM, Spadafori G. Veterinary Partner. VINcom. Published online August 8, 2017. Accessed February 1, 2023.
  15. Milk Thistle. Memorial Sloan Kettering Cancer Center. Published 2012. Accessed August 27, 2019.



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