A state-licensed compounding pharmacy that prepares customized medications for one patient at a time, against an individual prescription. 503A pharmacies are overseen mainly by state boards, not the FDA, and the products they compound are not FDA-approved. If you're considering a compounded GLP-1, knowing whether a 503A or a 503B made it tells you a lot about the manufacturing standards behind it.
Related terms: 503B outsourcing facility · Compounded medication · Salt form (semaglutide sodium / acetate)