How Products Were Selected:
Products selected represent those popular among readers of ConsumerLab.com and commonly sold and/or available nationally in the U.S. ConsumerLab.com purchased products on the open market through retail stores, on-line retailers and direct sales companies. Products were not accepted directly from manufacturers.Testing Methods:
Milk thistle products were analyzed in one or more independent laboratories for the following:- Total silymarin content (specifically the sum of isosilybin A and B, silybin A and B, silychristin and silydianin) by High Performance Liquid Chromatography (HPLC) methodology (USP36, DSC 2024).
- Yeast and mold (USP40, DSC-2024 <2023>) in products containing whole or milled seed.
- Analyses for lead, cadmium and arsenic by Inductively Coupled Plasma-Mass Spectroscopy (ICP/MS) for products containing whole herbs and/or more than 250 mg of minerals per daily dose.
- Disintegration time of tablets (excluding chewable, sublingual and time-release formulations) utilizing United States Pharmacopeia (USP) <2040> recommendations entitled "Disintegration and Dissolution of Nutritional Supplements."
- Disintegration time of enteric coated, time-release, and sustained release tablet, caplet and softgel formulations utilizing USP <2040> methodology for delayed-release (enteric-coated) tablets.
ConsumerLab.com may modify or use other appropriate test methods if necessary to test special product formulations.
Passing Score:*
To "Approved" by Consumerlab.com, a product must meet the following requirements:- Contain 100% of its minimum expected or claimed amount of total silymarin content, with a minimum of 2% silymarin (% wt./wt.) for powdered seed products (per USP40, DSC-2024) and a minimum of 58% silymarin (wt./wt.) for dry powdered extracts. Total silymarin is calculated as the sum of isosilybin A and B, silybin A and B, silychristin and silydianin. Extracts providing at least 58% silymarin but claiming a higher percentage (likely due to reliance on a non-specific test method not identified on the label) will be rated "APPROVED But Poor Labeling." Any product providing less than 100 mg of silymarin per serving will be noted as "Low Strength."
- Total combined mold and yeast count does not exceed 1,000 cfu/g (USP40, DSC-2024) in products containing whole or milled seed.
- Heavy Metals: Products containing whole herbs and/or more than 250 mg of minerals per daily dose must not exceed the following limits:
Lead:- Products marketed for use by children under 12 years of age or by pregnant or nursing women may not exceed the State of California's Prop 65 limits for lead in dietary supplements of 0.5 mcg per recommended daily serving with an additional allowance of 0.8 mcg if the product contains more than 1,000 mg/day of calcium. Products with a single serving weight of less than 5 grams that are not marketed for use by children under 12 years of age, may not exceed the State of California's Prop 65 limits for lead in dietary supplements of 0.5 mcg per recommended daily serving (above which a warning regarding reproductive harm, birth defects, or cancer risks is required in California) with an additional allowance of 0.4 mcg if containing 250-999 mg/day of any combination of elemental calcium, magnesium and potassium or 0.8 mcg if containing more than 1,000 mg/day of any combination of these minerals. An additional allowance of 0.5 mcg is provided if containing 250-999 mg/day of whole herb (not extract) or 1.0 mcg if containing 1000 mg/day or more of whole herb (not extract). However, total lead allowance must not exceed 2 mcg per daily serving.
- Products with single serving weights of 5 grams or more that are not marketed for children under 12 years of age may not exceed 2.5 mcg per serving nor 4.0 mcg per daily serving.
- Contain less than 10 micrograms of total arsenic per daily serving (based on Canada’s limit per daily serving of a natural health product, and U.S. EPA and state of New Jersey limit in 1 liter of water). Products found to exceed this amount were tested for inorganic arsenic and must not contain more than 2.1 micrograms of inorganic arsenic per daily serving (Canada's additional limit in natural health products).
- If marketed for use by children under 12 years of age, may not exceed 3.0 micrograms of cadmium per recommended daily serving (based on Canada's limit for a child weighing 75lbs). If not marketed for use by children under 12 years of age, may not exceed 4.1 micrograms of cadmium per recommended daily serving (above which California's Prop 65 law requires a "reproductive harm" warning due to developmental toxicity and male reproductive harm.
- May not exceed 2 micrograms of inorganic mercury per daily serving (based on EPA limit for mercury in 1 liter of water).
- If applicable to the product, must meet recommended USP <2040> parameters of disintegration for dietary supplements (excluding capsule, chewable, sublingual and time-release products).
- Enteric coated, time-release, and sustained release tablet, caplet and softgel formulations must meet recommended USP <2040> parameters for delayed-release (enteric-coated) tablets, caplets and softgels by visual inspection.
- Meet FDA labeling requirements.
