A 503B outsourcing facility is a compounder that registers with the FDA under Section 503B of the federal Food, Drug, and Cosmetic Act. Unlike a 503A pharmacy, it can produce larger batches without an individual prescription and must follow Current Good Manufacturing Practice (CGMP) standards and submit to FDA inspection.
This adds a layer of oversight above traditional 503A compounding, but a 503B product is still not the same as an FDA-approved manufactured drug: it has not gone through the FDA's review of safety and effectiveness for a specific product. Knowing whether a compounded medication comes from a 503A pharmacy or a 503B facility can help when weighing quality and risk with a prescriber.