A proprietary blend keeps each ingredient's dose out of view. Below we cover why makers use them, what they can conceal and why Trusted Health Reviews counts them against a product in every review.
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On a label, a proprietary blend groups several ingredients under one total amount and doesn't say how much of each is inside. You can't tell if any ingredient reaches the dose used in research, and a label can name popular ingredients at amounts too small to matter. In our reviews, undisclosed doses count as a negative.
Picture a label that reads 'Testosterone Support Matrix 750mg: KSM-66 Ashwagandha, Fenugreek Seed Extract, Zinc, Vitamin D3'. The combined amount is 750mg, but the split is unknown. Suppose it holds 600mg of ashwagandha (the top of the daily amount used in KSM-66 trials). That leaves just 150mg for the other three ingredients. If it holds 50mg of ashwagandha instead, the others share 700mg.
A common explanation is 'protecting the formula', since a fully disclosed formula is simple to copy. A blend also lets a maker include popular ingredients in very small amounts, and the buyer can't see that. A manufacturer confident in its product should print every individual amount on a transparent label.
When the amounts sit inside a proprietary blend, you can't work out whether each ingredient reaches its clinical dose, so you can't judge whether the product is likely to work. That is the core problem with proprietary blends.