Initial Posting: 1/16/2016    Last Update: 12/11/2019
Answer: ConsumerLab.com has long cautioned against purchasing supplements with proprietary formulas and typically does not test them. We may, however, check listed amounts of other key, individually listed ingredients in the same supplement. In some cases, we have found high levels of contaminants which, we suspect, originated from ingredients in a proprietary formula.
The major problem with "proprietary formulas," as well as with proprietary "blends" and "complexes," is that they permit manufacturers to withhold important information about what's really in a product. The company only has to list the total amount of formula, not the amount of each ingredient in the formula. The formula's ingredients only have to be listed in weight order, i.e., based on their relative contribution to the weight of the formula. Furthermore, the formula may change over time without you necessarily knowing.
Proprietary formulas are often developed around an expensive ingredient, like CoQ10, because this allows a company to use less of the expensive ingredient, creating a formula in which the expensive ingredient is just a small part of the formula. We have seen this with ingredients such as chondroitin in joint supplements, and SAMe. We also see proprietary formulas marketed for uses such as cognitive enhancement, nerve pain, or weight loss where a company may try to impress the consumer with a laundry list of ingredients having only shreds of evidence relating to the intended use. In most cases, the formulas themselves have not been clinically tested.