HOW PRODUCTS WERE EVALUATED:


How Products were Selected:



Products tested represent those commonly sold and/or available nationally in the U.S. ConsumerLab.com purchased products on the open market, such as through retail stores, on-line retailers and direct sales or multi-level marketing companies. Products were not accepted from manufacturers.

Testing Methods:


Milk thistle products were analyzed in one or more independent laboratories for the following:
  1. Total silymarin content (specifically the sum of dehydrosilybinin, isosilybinin A and B, silybinin A and B, silychristin and silydianin) by High Performance Liquid Chromatography (HPLC) methodology (USP36, DSC 2015).
  2. Yeast and mold (USP40 <2021>) in products containing whole or milled seed.  
  3. 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.
  4. Disintegration of non-chewable, non-capsule and non-time-release formulations utilizing United States Pharmacopeia (USP) <2040> methods. Any product not passing testing was sent to another independent laboratory to repeat testing for the criterion on which it did not pass.
ConsumerLab.com may modify or use other appropriate test methods if necessary to test special product formulations.

The identities of the products were not disclosed to the laboratories performing the testing.

Passing Score:*


To "Approved" by Consumerlab.com, a product must meet the following requirements:
  1. Contain 100% of its minimum expected or claimed amount of for total silymarin content, with a minimum of 2% silymarin (% wt./wt.) for powdered seed product (per USP40) and a minimum of 58%% silymarin (wt./wt.) for dry powdered extracts. Total silymarin is calculated as the sum of dehydrosilybinin, isosilybinin A and B, silybinin 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."
  2. Total combined mold and yeast count does not exceed 102 cfu/g in products containing whole or milled seed.
  3. 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 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 weights of less than 5 grams which are not marketed for use by children, may not exceed the State of California's Prop 65 limits for lead in dietary supplements 0.5 mcg per recommended daily serving 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 to 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 will not exceed 2 mcg.
    • Products with single serving weights of 5 grams or more which are not marketed for children may not exceed 2.5 mcg per serving nor 4.0 mcg per daily serving.
    Cadmium**:
    • If marketed for use by children, may not exceed 3.0 micrograms of cadmium per recommended daily serving (based on Canada's limit for a child weighing 75 lbs.). If not marketed for use by children, may not exceed 4.1 micrograms of cadmium per recommended daily serving (based on the State of California's Prop 65 limit).
    Arsenic:
    • Contain less than 10 micrograms of total arsenic and no more than 5 micrograms of inorganic arsenic per daily serving (EPA limit - based on 1 liter of water).
  4. If applicable to the product, must meet recommended USP <2040> parameters of disintegration for dietary supplements (excluding capsule, chewable, sublingual and time-release products).
  5. Be in compliance with FDA labeling requirements.
A "Pass" was based on meeting the above criteria in either the first or second rounds of testing.

* Passing scores allow for specific margins of technical error associated with each analysis. ConsumerLab.com reserves the right to disqualify a product at any time from passing its testing if it considers such product to display unacceptable variation in quality, present a safety risk or to provide misleading or inaccurate information in its labeling.

** Based on state of California's Prop 65 limits. California requires supplements exceeding this limit to bear a warning label regarding lead.

Back to review