Milk Thistle: Quality Update

This article is part of a series that discuss, in depth, quality-related issues around a specific ingredient.

Here’s a bit of information about milk thistle that you HAVE to hear.  A recent publication in has highlighted the flaws in many Milk Thistle supplements – even ones from some “Vitality Approved” brands.

For example, Bluebonnet and Pure Encapsulations are tremendous vitamin companies.  But because they don’t meet our standards as it pertains to herbs, we do not use or sell their herbal products.  In our view, a brand can be great at a certain category of products and therefore be “Vitality Approved” for those products only. 

The United States Pharmacopoeia (USP) is the body that governs the quality control of supplements.  They do so by setting basic standards for supplement testing, which manufacturers SHOULD follow but are NOT required to.  A “USP Verified” seal does not necessarily make a product good – it is a single measure of quality that is far from comprehensive.  Secondly, USP testing recommendations are insufficient for most herbs, as they do not cover a lot of possible adulteration issues.

link to infographic about milk thistle quality

Case in point: USP states that milk thistle products should be tested with HPLC and UV-vis, which are specialized testing mechanisms that identify what compounds are in a given product.

Unfortunately, UV-vis actually overestimates the amount of the active compound silymarin found in a milk thistle product.  The UV-vis testing method is not specific to silymarin and identifies other compounds as silymarin.  That means a sub-potent product could be reported as potent.

Many manufacturers are buying products that are claiming to be “80% silymarin UV-vis.”  According to ConsumerLab, many of these are substandard, cheap Chinese raw materials suppliers.  When analyzed with a more accurate measure (in this case, the HPLC), it is found that the “80% silymarin” is actually a lot less!

Seven of the 11 companies ConsumerLabs tested failed potency testing for milk thistle.  This shows the widespread quality problem in the supplement industry.  A majority fail because they are using substandard ingredients from shady sources.  Most importantly, they are not then verifying the raw materials and instead of taking the supplier’s word.  Raw materials should be quarantined and tested to validate they are what they say they are.

It’s all about cost.  HPLC verified milk thistle costs much more than the “80% UV-vis” form.  This profit gets paid for by the consumer, who puts trust in an industry that doesn’t deserve it.

ConsumerLabs puts it succinctly:  “The FDA does not set standards for the composition of herbal products or how manufacturers are supposed to test them. Consequently, manufacturers may choose to use any form of milk thistle and consumers normally have no way of knowing the quality of what they are buying.”

Milk Thistle Contamination

What’s worse is the contaminants found in many batches of milk thistle raw materials recently.  When properly tested using mass spectrometers, milk thistle batches are found to have gasoline.  Yes, like the stuff that makes cars go.

What is gasoline doing there?  It’s an industrial contaminant from the careless, cheap processing of natural products that happens all across the globe.  Other times we’ve seen similar harsh chemicals like hexane in herbs, usually used as a cheap solvent to extract out the active ingredient from herbs.

If you are lucky enough to get a potent milk thistle product, which by the ConsumerLabs report puts your success at 36%, you then have to be concerned with horrible contaminants such as gasoline!

Quality Must Come First

This is why we are nuts about quality.  The Milk Thistle we select for herbs MUST use whole herbs – not powders – to prevent 90% of adulteration or contamination that can happen.  Their extraction methods MUST be clean and appropriate to the herb in question.  The company must make a commitment to quality above all else.

Just trying to keep it real…

Neal Smoller, PharmD
Owner, Pharmacist, Big Mouth

Dr. Neal Smoller, Holistic Pharmacist

About Neal Smoller

Dr. Neal Smoller, PharmD, is a licensed pharmacist: and owner of Village Apothecary, an independent pharmacy in the most famous small town in America—Woodstock, NY. He’s also the host of the popular wellness podcast, The Big Mouth Pharmacist.”


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