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Silymarin (ATC A05BA03) is a hepatoprotective flavonolignan complex from milk thistle (Silybum marianum), used as supportive therapy in chronic liver diseases and generally considered compatible with breastfeeding, though human lactation data remain limited and warrant cautious use.medpedia.framar+5

Active substance and ATC class

Silymarin is a semi-synthetic preparation obtained from the fruits/seeds of milk thistle, composed mainly of silibinin, silidianin and silicristin.mims+3
It is classified in ATC group A05BA “Liver therapy”, at the specific 5th level A05BA03; preparations containing silibinin share the same 5th level as silymarin.atcddd.fhi+1

Indications and clinical use

Medicinal products containing silymarin are used as supportive treatment in acute and chronic hepatitis, liver steatosis, toxic liver injury and cirrhosis, including drug‑ and alcohol‑induced liver damage.medanta+3
Evidence from clinical and experimental studies shows hepatoprotective, antioxidant and antifibrotic effects in chronic liver diseases, although some data are heterogeneous and not fully conclusive.pmc.ncbi.nlm.nih+3

Pharmacodynamics and mechanism of action

Silymarin stabilizes hepatocyte cell membranes, limiting the entry of hepatotoxic substances, and scavenges free radicals, thereby reducing oxidative stress and lipid peroxidation.cureus+3
It can increase intracellular glutathione, stimulate protein synthesis and hepatocyte regeneration, and may modulate inflammatory and fibrogenic pathways in chronic liver disease.scholar.cu+3

Pharmacokinetics and bioavailability

Orally administered silymarin has relatively low bioavailability, estimated around 20–50%, largely due to poor solubility and extensive first‑pass metabolism with phase II conjugation.scholar.nycu+1
It undergoes multiple conjugation reactions and biliary excretion; formulations such as phytosomes have been developed to enhance absorption and systemic exposure.scholar.nycu+1

Dosage and administration

Typical adult oral doses for hepatoprotection range from 420–600 mg per day, often divided into two or three doses and taken with food to optimize absorption.medpedia.framar+2
In clinical practice and product information, regimens such as 140 mg twice or three times daily, or 140 mg three times daily in cirrhosis, are commonly used for at least several weeks to months.mims+2

Adverse effects and general toxicity

Silymarin has an overall favourable safety profile, with gastrointestinal symptoms (nausea, diarrhoea, dyspepsia, abdominal discomfort, bloating, flatulence) and headache among the more frequently reported adverse reactions.pubmed.ncbi.nlm.nih+4
Allergic manifestations such as pruritus and rash have been described, and very high oral doses (up to 700 mg three times daily for 24 weeks) were generally well tolerated without major toxicity in clinical trials.medanta+2

Contraindications and cautions

Contraindications include hypersensitivity to silymarin or excipients; some formulations contain wheat starch and lactose, making them unsuitable for patients with coeliac disease or lactose intolerance.medpedia.framar
Although animal and human data suggest low toxicity and good tolerability, caution is advised in pregnancy and in patients receiving drugs with a narrow therapeutic index because of potential pharmacokinetic interactions.cureus+2

Drug–drug interactions

Experimental data show that silymarin can inhibit certain cytochrome P450 isoenzymes, UDP‑glucuronosyltransferases and P‑glycoprotein, which may alter the disposition of co‑administered drugs, even though many in‑vivo studies find limited clinically relevant effects.sciencedirect+2
Clinically, reduced efficacy of oral contraceptives and possible potentiation of drugs such as benzodiazepines (e.g. diazepam, alprazolam), some cytotoxic agents (e.g. vinblastine) or other concomitant medicines have been reported, so health professionals should monitor for interactions and adjust therapy as needed.pubmed.ncbi.nlm.nih+2

Pregnancy safety considerations

One clinical trial in pregnant women and preclinical studies suggest that silymarin can be used without evident teratogenicity or major maternal toxicity, but the overall data set remains limited.herbalgram+2
Consequently, silymarin in pregnancy is generally considered low‑toxicity but should be reserved for clear indications, with individualized risk–benefit assessment and preference for products with established quality and dosing.herbalgram+2

Lactation and breast milk transfer

Available evidence indicates that silymarin or milk thistle extracts are excreted into breast milk in little or negligible amounts, and specialized lactation resources classify milk thistle as “very low risk” and compatible with breastfeeding.e-lactation+1
Nonetheless, high‑quality human data on infant exposure and long‑term outcomes are scarce; authoritative reviews advise that nursing mothers use silymarin cautiously, preferably under medical supervision, and avoid unnecessary supplementation when safer alternatives exist.droracle+2

Toxicological‑lactological assessment (ATC A05BA03)

From a toxicological standpoint, silymarin shows low acute and chronic toxicity, absence of major genotoxic effects at therapeutic concentrations, and good human tolerability even at high doses, with adverse effects mainly mild and reversible.pmc.ncbi.nlm.nih+2
From a lactological perspective, silymarin‑containing medicines in ATC A05BA03 can generally be considered compatible with breastfeeding when used at standard hepatoprotective doses, but due to limited controlled human data, monitoring of the breastfed infant and avoidance of off‑label high‑dose or long‑term use purely as a galactogogue are recommended.semanticscholar+3