Silymarin / Milk Thistle
Silybum marianum extract (silibinin, silybin)
Also known as: Denamarin · Legalon · Doxion · Hepaticare · Hepatosupport · Hepatosyl Plus · Samylin · Zentonil Advanced · Milk Thistle · Silybum marianum · Carduus marianus · Holy Thistle · Marian Thistle · Silibinin · Silybin · Sylibin · Silibide · Silymarin
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Therapeutic dosage (general) | 50-250 mg/day | PO | q24h | — | 🌎 NA |
| Adjunctive therapy for chronic liver disease | 20-50 mg/kg per day | PO | q24h | — | 🌎 NA |
| Chronic liver disease and ameliorating the effects of anticonvulsants | 50-200 mg | PO | q12-24h | — | 🌎 NA |
| Hepatotoxicity, hepatic recovery/regeneration, hepatic fibrosis | 20-50 mg/kg/day | PO | q24h | — | 🌎 NA |
- Therapeutic dosage (general): Suggested dose range
- Adjunctive therapy for chronic liver disease: Extrapolated from human, monkey, rodent and dog research
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Therapeutic dosage (general) | 50-250 mg/day | PO | q24h | — | 🌎 NA |
| Adjunctive therapy for chronic liver disease | 20-50 mg/kg per day | PO | q24h | — | 🌎 NA |
| Chronic liver disease and ameliorating the effects of anticonvulsants | 50-200 mg | PO | q12-24h | — | 🌎 NA |
| Hepatotoxicity, hepatic recovery/regeneration, hepatic fibrosis | 20-50 mg/kg/day | PO | q24h | — | 🌎 NA |
| General hepatic support | 4-8 mg/kg/day | PO | q24h | — | 🌎 NA |
- Therapeutic dosage (general): Suggested dose range
- Adjunctive therapy for chronic liver disease: Extrapolated from human, monkey, rodent and dog research
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Silymarin is a flavonolignan complex extracted from the seeds of the milk thistle plant (Silybum marianum). It is widely utilized in veterinary medicine as a hepatoprotective nutraceutical.
- Primary Uses: Management of acute and chronic hepatopathies, cirrhosis, and inflammatory liver diseases in dogs, cats, and other species.
- Toxin Antidote: Particularly noted for its critical role as a hepato-protective agent following the ingestion of severe hepatotoxins, such as Amanita phalloides (death cap mushrooms).
- Oncology Support: Emerging laboratory data suggests it may help prevent certain cancers and reduce the hepatotoxic side effects of specific chemotherapy protocols.
Clinical Pearl: Because silymarin is a nutraceutical, over-the-counter product quality and bioavailability vary wildly. Veterinary-specific formulations where silybin is complexed with phosphatidylcholine (phytosomes) are highly recommended due to vastly superior gastrointestinal absorption compared to standard extracts.
Mechanism of action
Silymarin exerts its hepatoprotective effects through multiple synergistic pathways. Silibinin (or silybin) is the most biologically active component of the complex.
- Antioxidant & Free Radical Scavenging: Inhibits lipid peroxidase and beta-glucuronidase. It directly scavenges reactive oxygen species (ROS) and significantly increases intracellular glutathione levels in the liver.
- Membrane Stabilization: Alters the outer hepatocyte cell membrane structure, competitively blocking the binding and transmembrane transport of hepatotoxins (e.g., amatoxins from poisonous mushrooms).
- Anti-inflammatory: Inhibits the cytotoxic, inflammatory, and apoptotic effects of Tumor Necrosis Factor-alpha (TNF-α) and modulates leukotriene synthesis.
- Antifibrotic: Reduces hepatic stellate cell activation, thereby decreasing hepatic collagen formation and slowing the progression of cirrhosis.
- Regenerative: Stimulates ribosomal RNA polymerase A → enhances protein synthesis and accelerates hepatocyte regeneration.
Safety & warnings
Contraindications
- Known hypersensitivity or allergy to the Asteraceae/Compositae plant family (ragweed, marigolds, daisies)
- Use caution with whole plant extracts (not the seed extract) in patients where exogenous estrogens are contraindicated, due to potential estrogen-like activity
Adverse effects
- Gastrointestinal upset (mild nausea, vomiting, diarrhea)
- Allergic reactions in patients sensitive to the Asteraceae/Compositae plant family
- Generally very well tolerated
- Rare mild gastrointestinal upset
Precautions
Important Warning: Do not confuse Milk Thistle with Blessed Thistle, which is a completely different botanical compound.
- Regulatory Status: These products are considered nutritional supplements and are not evaluated or approved by the FDA as pharmaceuticals. Potency and purity can vary between manufacturers.
- Pregnancy/Nursing: Safety data during pregnancy or nursing is unavailable; weigh potential benefits against uncertain risks.
Drug interactions
Silymarin may inhibit cytochrome P450 isoenzyme 2C9 (CYP2C9). Use caution with narrow therapeutic index drugs metabolized by this pathway.
May inhibit CYP3A4, though clinical significance is currently undetermined.
Silymarin may increase the clearance of these drugs (not applicable in cats). Clinical significance is undetermined.
Monitoring
- Clinical efficacy (resolution of clinical signs)
- Liver enzyme panels (ALT, AST, ALP, GGT)
- Hepatic function tests (Bilirubin, Bile Acids, BUN, Albumin)
- Liver enzymes (ALT, AST, ALP, GGT)
- Total bilirubin
- Clinical signs of hepatic disease (e.g., icterus, lethargy, appetite)
Pharmacokinetics
Absorption
In humans, oral bioavailability is <50% with peak levels occurring 2-4 hours post-dose. Silymarin is fairly insoluble in water. When silibinin is complexed with phosphatidylcholine (phytosome technology), oral absorption is significantly increased.
Distribution
Undergoes extensive enterohepatic circulation. Achieves significantly higher concentrations in liver cells and bile compared to plasma.
Metabolism
20-40% is converted into glucuronide and sulfate conjugates.
Elimination
The majority of the drug is eliminated unchanged in the feces. Conjugates are also eliminated in the feces. Only about 8% is excreted in the urine. Elimination half-life in humans averages 6 hours.
Overdose
Overdoses are highly unlikely to cause significant morbidity due to the supplement's high safety margin. Mild gastrointestinal effects (vomiting, diarrhea) may be seen and should be treated in a supportive and symptomatic manner.
Available products
Formulations
- Chewable tablets
- Capsules
- Oral tablets: 9 mg, 24 mg, 25 mg, 35 mg, 40 mg, 50 mg, 70 mg, 100 mg
- Oral powder: 10 mg, 40 mg, 53 mg
Veterinary
- Marin for Cats (Silybin A+B 9 mg in a phosphatidylcholine complex & Vitamin E 50 Units Tablets)
- Marin for Dogs (Small/Medium) (Silybin A+B 24 mg in a phosphatidylcholine complex, Vitamin E 105 Units, & Zinc 17 mg Chewable Tablets)
- Marin for Dogs (Large) (Silybin A+B 70 mg in a phosphatidylcholine complex, Vitamin E 300 Units, & Zinc 45 mg Chewable Tablets)
- Denamarin (Combination product containing SAMe and silybin)
- Doxion
- Hepaticare
- Hepatosupport
- Hepatosyl Plus
- Samylin
- Zentonil Advanced
Human-labeled
- Various OTC nutritional supplements (tablets and capsules ranging from 150-1000 mg). Look for products stating a standardized concentration of 70-80% silymarin.
- Various authorized proprietary products
Regulatory status
Authorized Veterinary Medicine - General Sales List (General sale)
Authorized Veterinary Medicine - General Sales List (General sale)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Unless otherwise labeled, commercially available products containing silymarin should be stored at room temperature in tight containers. Avoid storing the products in areas of high humidity.
Client information
What is Silymarin? Silymarin (Milk Thistle) is a natural nutritional supplement used to support and protect your pet's liver from damage, reduce inflammation, and promote liver healing.
- Administration: Can be given with or without food. If your pet experiences stomach upset, try giving the supplement with a small meal or treat.
- Side Effects: This supplement is generally very safe. It may occasionally cause mild diarrhea or vomiting. If these signs persist or become severe, contact your veterinarian.
- Patience is Key: Because it is a supportive therapy, it may take several weeks of consistent use to see improvements in your pet's bloodwork or clinical condition.
- Quality Matters: Since it is not an FDA-regulated drug, product quality varies. It is highly recommended to use the specific veterinary brand prescribed by your vet, as these are formulated for better absorption in pets.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.