USP <797> is the chapter of the United States Pharmacopeia that sets the minimum standards for preparing sterile medications — injectables, eye drops, and similar products — in a pharmacy. It covers the cleanroom environment, staff training and garbing, air quality, cleaning, and how long a preparation may be used before it is discarded. State boards of pharmacy adopt it, which is what makes it enforceable for a traditional 503A compounding pharmacy.
It matters for compounded GLP-1s because those are sterile injectables. A 503A pharmacy is not required to follow the FDA's current good manufacturing practice (CGMP) rules that drug manufacturers and 503B outsourcing facilities must meet; USP <797> is the standard it follows instead. Asking a pharmacy whether it complies with USP <797> — and whether the state board has inspected it — is one of the most concrete legitimacy checks available. See talking to a pharmacist about compounded medications and how compounded GLP-1 medications are made.