# Silymarin (Milk Thistle / Silybin): veterinary dose and monograph

> Silymarin (Milk Thistle / Silybin) is a veterinary gastrointestinal drug. A flavonolignan complex from milk thistle (Silybum marianum), whose principal active is silybin (silibinin) — a long-standing herbal HEPATOPROTECTANT and antioxidant. Indications include chronic hepatitis / cholangitis and toxic/drug-induced hepatopathy — antioxidant hepatoprotection; amanita (death-cap) and other hepatotoxic mushroom poisoning (silibinin) — adjunct; aflatoxicosis / hepatotoxin exposure support. This monograph lists 2 reference doses for dogs and cats, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/silymarin · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Gastrointestinal
- **Also known as:** Silibinin, Silybin, Legalon, Milk thistle extract
- **Species with doses:** Dogs and Cats
- **General dose range:** 20–50 mg/kg PO q12–24h — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Chronic hepatitis / cholangitis and toxic/drug-induced hepatopathy — antioxidant hepatoprotection
- Amanita (death-cap) and other hepatotoxic mushroom poisoning (silibinin) — adjunct
- Aflatoxicosis / hepatotoxin exposure support
- General hepatic antioxidant support (often with SAMe)

## Silymarin (Milk Thistle / Silybin) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Silymarin (Milk Thistle / Silybin) doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Hepatoprotection / toxic hepatopathy | 20–50 mg/kg | PO | per day (once daily or divided q12h) | — |

- Hepatoprotection / toxic hepatopathy: Plumb’s p.1062: 20–50 mg/kg per day for chronic liver disease or hepatotoxicity (Center; Webb); 50–250 mg per day (Twedt). Papich 5e: 5–15 mg/kg PO once daily (some sources a minimum of 30 mg/kg/day). Lower doses apply to the more bioavailable silybin–phosphatidylcholine complex. Therapeutic dose not firmly established.

### Cats

*Silymarin (Milk Thistle / Silybin) doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Hepatoprotection / cholangitis / lipidosis | 4–15 mg/kg | PO | q24h | — |

- Hepatoprotection / cholangitis / lipidosis: Plumb’s p.1062 (Zoran 2006): cats 4–8 mg/kg/day. Papich 5e (dogs and cats): 5–15 mg/kg PO once daily. Therapeutic dose not firmly established.

### Horses

*Silymarin (Milk Thistle / Silybin) doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| No reference dose for this species | Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species | — | — | — |

- No reference dose for this species: Papich 5e states no clinically effective dose has been reported in horses (6.5–26 mg/kg q12h produced only minor antioxidant effects); Plumb’s gives no horse dose.

## Contraindications

Known hypersensitivity to milk thistle/Asteraceae. Few true contraindications (well-tolerated). Note variable potency/standardisation of OTC "milk thistle" products — prefer standardised silybin formulations.

## Adverse effects

- Very well tolerated
- Occasional GI upset (loose stool) at high doses
- Mild laxative effect

## Drug interactions

- Complementary with SAMe and N-acetylcysteine (layered antioxidant hepatoprotection)
- May mildly inhibit some CYP/UGT enzymes at high doses (theoretical effect on co-metabolised drugs)
- No major adverse interactions of clinical note

## Pregnancy and lactation

Considered low-risk; use if clearly indicated.

## Monitoring

- Liver enzyme/bilirubin trends and clinical response
- Use a standardised/bioavailable formulation (silybin-phosphatidylcholine) for reliable effect
- Part of a broader hepatic plan (treat the underlying disease)

## Toxicity and overdose

Very wide safety margin — overdose typically causes only mild GI upset / loose stool. No characteristic organ toxicity. The practical limitation is the POOR bioavailability of plain silymarin (hence the preference for the silybin-phosphatidylcholine complex), not toxicity.

Management: Supportive only; no specific antidote needed (wide margin). Manage any GI upset symptomatically.

## Clinical pearls

- The classic herbal hepatoprotectant — antioxidant, membrane-stabilising and regeneration-supporting; famous as silibinin for Amanita (death-cap) mushroom poisoning
- Bioavailability of plain "milk thistle" is poor — use the silybin-phosphatidylcholine complex (e.g. Marin/Denamarin) for a reliable effect
- Layers well with SAMe and N-acetylcysteine for antioxidant hepatoprotection
- Very safe, but it is supportive — diagnose and treat the underlying liver disease

## Mechanism of action

Silybin and the other silymarin flavonolignans act as antioxidants (scavenging free radicals and boosting glutathione/superoxide-dismutase), stabilise hepatocyte cell membranes against toxin entry (notably blocking the OATP-mediated uptake of amatoxins in Amanita poisoning), inhibit lipid peroxidation, stimulate ribosomal protein/RNA synthesis to aid hepatocyte regeneration, and exert anti-inflammatory and anti-fibrotic effects on the liver. The net effect is protection of liver cells from oxidative and toxic injury and support of regeneration.

## Formulations and products

- Silymarin extract capsule/tablet (standardised)
- Silybin–phosphatidylcholine complex (Marin/Denamarin component)
- Marin / Denamarin (silybin + SAMe) (Nutramax) — Silybin-phosphatidylcholine (± SAMe), Tablet
- Livfit Suspension (Bionex Vetcare Pvt Ltd, Thane (MH)) — Silymarin 70 mg + Tricholine citrate 100 mg + Vitamin B complex 19.6 mg + L-Ornithine 10 mg + Cysteine 2 mg + Quercetin 2 mg + Selenium dioxide 30 mcg per 10 mL, Oral suspension
- Legalon / Silybon — 70 / 140 mg silymarin, Capsule / tablet (human-label)

## Storage

Capsules/tablets: 15–30 °C, dry, protect from light. Prefer standardised silybin products.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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## Frequently asked questions

### What is the dose of Silymarin (Milk Thistle / Silybin) for dogs?

Reference doses for Silymarin (Milk Thistle / Silybin) in dogs: 20–50 mg/kg PO per day (once daily or divided q12h) (Hepatoprotection / toxic hepatopathy). Confirm against the label and the patient before use.

### What is the dose of Silymarin (Milk Thistle / Silybin) for cats?

Reference doses for Silymarin (Milk Thistle / Silybin) in cats: 4–15 mg/kg PO q24h (Hepatoprotection / cholangitis / lipidosis). Confirm against the label and the patient before use.

### Can Silymarin (Milk Thistle / Silybin) be given to horses?

Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species (No reference dose for this species).

### When should Silymarin (Milk Thistle / Silybin) not be used?

Known hypersensitivity to milk thistle/Asteraceae. Few true contraindications (well-tolerated). Note variable potency/standardisation of OTC "milk thistle" products — prefer standardised silybin formulations.

### What are the side effects of Silymarin (Milk Thistle / Silybin) in animals?

Very well tolerated; Occasional GI upset (loose stool) at high doses; Mild laxative effect.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.