It's not a bad place to start but it's certainly not a guarantee you are getting the best product. USP stands for The United States Pharmacopoeia. The USP was developed so that synthetic compounds (drugs) have an established manufacturing and testing protocol that when followed the finished product will yield consistent results.
Since then there has been a supplement manufacturing/testing program that sets guidelines for manufacturing, but those guidelines only assure you of purity, potency, stability and disintegration, not overall effectiveness of the product claims. So at the very least the USP stamp gives you the ingredients you were looking for. But proper dosages, ingredient forms and delivery systems (getting the ingredients to the right tissues at the right time in the right amounts) often goes away from USP guidelines in order to make the product better. And these innovative manufacturers hesitate to disclose their trade secrets. If the consumer looks for the USP as a stamp of approval when purchasing dietary supplements, they have only eliminated the bad guy that may not be following the minimum available guidelines that everyone should adhere to. Unfortunately they may have also decreased their chances of acquiring a product that had incorporated the latest science and technology during manufacturing, giving the compound the greatest potential to yield the desired result. Your best bet to assure what you are purchasing has the greatest potential to work is to have the manufacture supply the following:
• Best, current clinical research supporting use of active ingredients (evidence-based)
• Show data supporting safety and efficacy including long-term empirical data
• Identify proper ingredient dosage and forms matched to positive outcomes from clinical data
• All dietary supplement products and powders should be manufactured in a FDA-registered pharmaceutical facility, in compliance with Good Manufacturing Practices (GMP)
• Ingredients all tested for purity, potency and delivery from raw materials to finished product