503A and 503B are two sections of the Federal Food, Drug, and Cosmetic Act, and each describes a different kind of compounder. A 503A pharmacy is the familiar kind: a state-licensed pharmacy mixing a drug for one patient on a prescription. A 503B outsourcing facility is closer to a small manufacturer, registered with FDA and held to manufacturing standards.
For a buyer, the tier decides who inspects the pharmacy and what quality rules apply, and it can shape the price. It is also why some peptides can be filled by one tier and not the other, which is part of why the price boards list the compounds they do.
| 503A pharmacy | 503B outsourcing facility | |
|---|---|---|
| Who | Licensed pharmacist in a state-licensed pharmacy, or a physician | A facility that elects to register with FDA |
| Prescription | For an identified individual patient | May or may not obtain patient prescriptions; may supply office stock |
| Manufacturing standard (CGMP) | Exempt | Required |
| Primary oversight | State board of pharmacy | FDA, on a risk-based inspection schedule |
| Must be a licensed pharmacy | Yes, unless a physician or a federal facility compounds | No |
| Bulk substances allowed | USP monograph, component of an approved drug, or on the 503A list | On the 503B clinical-need list, or the drug is in shortage |
| Reports to FDA | Not required to report adverse events | Reports products twice a year and reports adverse events |
503A: the pharmacy that fills your prescription
Section 503A exempts a compounded drug from FDA approval when a licensed pharmacist in a state-licensed pharmacy, or a physician, compounds it for an identified individual patient on a valid prescription[1].
A 503A pharmacy may compound from a bulk substance only in three cases[1]. The substance has a USP or NF monograph, or it is a component of an FDA-approved drug, or it appears on FDA’s 503A list. Each bulk substance must also come with a valid certificate of analysis[1], which the peptide COA guide explains.
State boards of pharmacy have primary responsibility for day-to-day oversight of these pharmacies[3]. FDA conducts surveillance and for-cause inspections of them as well[3]. Federal law does not require these pharmacies to report adverse events to FDA[7].
503B: the outsourcing facility
Section 503B was created by the Drug Quality and Security Act in November 2013[4]. An outsourcing facility is one location, engaged in compounding sterile drugs, that has elected to register and complies with the section[2]. It is not required to be a licensed pharmacy[2].
The practical difference for a buyer is scale and standards. An outsourcing facility may or may not obtain prescriptions for individual patients, so it can supply clinics with office stock ahead of need[5]. In exchange, it must meet current good manufacturing practice requirements and is inspected by FDA on a risk-based schedule[4].
FDA states the CGMP contrast plainly in a May 2026 notice: section 503A exempts compounded drugs from CGMP requirements, and section 503B provides no such exemption[5]. An outsourcing facility also reports its products to FDA every June and December[2], and reports adverse events[4].
What the tier means for what you pay
Neither tier makes a compounded drug FDA-approved. FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed, whichever tier made them[3]. What the tier changes is the quality system and the inspector.
Oversight varies in practice. A secret-shopper study of clinics selling compounded GLP-1s traced 23 supplying compounders, and 4 of 21 checked (19.0%) were not licensed for sterile compounding[6]. Three of 22 (13.6%) had faced state disciplinary action since 2023[6].
So the useful question for a seller is not only the price but the pharmacy’s name and tier. That is also how to read a quote for compounded semaglutide or compounded tirzepatide, where the tier decides whether the drug can be made at all. The fees around the drug are in the peptide therapy cost guide.