Sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act describe two ways to compound a drug lawfully in the United States. A 503A pharmacy compounds for an identified patient on a prescription and is exempt from the manufacturing rules because of it. A 503B outsourcing facility registers with FDA, follows current good manufacturing practice, and may compound without a prescription for office use. The gap between them is not a matter of degree; it is a different regulator, a different rulebook, a different cost base and a different customer.
Where the two sections came from
Section 503A dates from the FDA Modernization Act of 1997 and was clarified by the Drug Quality and Security Act of 2013. Section 503B was created by the DQSA after the 2012 fungal meningitis outbreak traced to contaminated steroid injections from a compounding pharmacy that was, in practice, manufacturing at scale without a manufacturer's controls. Congress created the outsourcing facility category so that large-scale compounding for hospitals and clinics would happen under FDA oversight and cGMP, while leaving traditional patient-specific compounding with the state boards. Everything else on this page follows from that split.
Side by side
| 503A compounding pharmacy | 503B outsourcing facility | |
|---|---|---|
| Primary regulator | State board of pharmacy; FDA may inspect | FDA; state licensure may also apply |
| Must be a licensed pharmacy? | Yes (or a physician) | No, but compounding must be by or under direct supervision of a licensed pharmacist |
| Patient-specific prescription | Required (limited anticipatory compounding allowed on history) | Not required; may compound office stock |
| cGMP (21 CFR 210/211) | Exempt; USP <795>/<797>/<800> apply | Required; USP chapters are a floor |
| FDA registration | None | Annual registration and establishment fee |
| Reporting to FDA | None routine | Product reports each June and December; adverse event reports |
| Bulk substances | USP/NF monograph, component of approved drug, or 503A bulks list | 503B bulks list (Category 1 while under evaluation) or drug shortage list |
| Essentially a copy | Not regularly or in inordinate amounts | Not at all unless a clinical difference is documented or the drug is in shortage |
| Labeling | State board and USP requirements | Statutory elements: "This is a compounded drug", lot, BUD, facility, storage, and for office stock "Not for resale" |
| Interstate distribution | 5% of prescriptions unless the state has signed FDA's MOU | No statutory percentage cap |
| Inspection | State board; FDA for cause | FDA risk-based; results published |
| Release testing | Per USP chapter and category; sterility testing for some Category 2/3 CSPs | Per batch per 21 CFR 211.165 and your specifications |
| Quality system | USP QA/QC programme | Independent quality unit; deviations, CAPA, change control, stability under 211 |
| Typical customers | Patients, prescribers for patient-specific use | Hospitals, surgery centres, clinics for office use; patients too |
503A in practice
A 503A pharmacy's day is prescription-driven: receive, check eligibility (state licence, controlled-substance rules), pharmacist verification, compound or fill from a small anticipatory lot, pack, ship. Its compliance exposure is in the volume of small decisions — refill limits, nonresident licences, BUDs, documentation of each fill — and its inspections come from the state board, PCAB if accredited, and occasionally FDA. It may compound limited quantities before receiving prescriptions based on its dispensing history, but it cannot sell office stock to a clinic. Shipping out of state is capped at 5% of total prescriptions unless the destination state has signed FDA's memorandum of understanding, which most states have. The 503A software page lists the rules the platform applies for this model.
503B in practice
A 503B's day is batch-driven: plan a batch from an approved formulation, consume raw-material lots with quantities recorded, produce a finished lot into quarantine, test it against specifications, release it on a QA signature, serialize and distribute. It has an independent quality unit, an environmental monitoring programme, a stability programme supporting each labeled BUD, and a document set that would look familiar in any small pharmaceutical plant. FDA inspects on a risk-based schedule and publishes the outcome; hospital purchasing departments read those outcomes. The cost base is much higher — facility qualification, per-batch testing, quality staff — which is why 503Bs run narrower catalogues at higher volume. The 503B software page describes the batch record and release interlock; the launch playbook covers building one.
The grey areas: office stock, copies, interstate
Three questions cause most of the confusion.
Can a 503A supply office stock?
Not for administration to patients without a prescription. Anticipatory compounding under 503A is for prescriptions the pharmacy reasonably expects to receive, in limited quantities; a clinic that wants vials on the shelf for whoever walks in needs a 503B. Some states have carved out narrow allowances for office-use compounding under state law, and FDA has said it does not intend to treat these as exempt under 503A; treat this as a matter for regulatory counsel in your state.
What is "essentially a copy"?
For a 503A, compounding a drug that is essentially a copy of a commercially available drug is prohibited when done regularly or in inordinate amounts; a prescriber's documented determination that the compounded drug produces a significant difference for the patient takes it outside the definition. For a 503B the rule is stricter: no copies at all unless the prescriber documents a clinical difference for the individual patient or the approved drug is on FDA's shortage list. FDA issued separate guidance documents for each section in 2018. GLP-1 compounding through and after the semaglutide and tirzepatide shortages turned on exactly this question.
How much can a 503A ship across state lines?
Five percent of total prescription orders dispensed or distributed, unless the state in which the pharmacy is located has entered into FDA's standard MOU, which raises the threshold and adds reporting by the state. A 503B has no statutory percentage cap but must hold whatever nonresident licences the destination states require.
Which should you be?
- 1Who is the customer?
Individual patients on prescriptions — 503A. Hospitals and clinics wanting stock on the shelf — 503B. Both — read the next section.
- 2What is the volume per product?
Hundreds of unique prescriptions a day across many formulations suits a 503A. Thousands of identical units of a few products suits a 503B, because per-batch testing and stability work amortise over volume.
- 3Can you fund a quality unit and a qualified facility?
A 503B needs an independent head of quality, a qualified cleanroom, per-batch release testing and a stability programme before the first commercial batch. If the answer is not yet, start as a 503A.
- 4Can you live with published inspection results?
FDA publishes 503B inspection classifications, 483s and warning letters. Your customers will read them.
- 5Which products?
Check each candidate against the 503A or 503B bulks list, the copies guidance for that section, and the NIOSH list. Some products are viable under one section and not the other.
Running both
A single registered outsourcing facility cannot also be a 503A; but one organisation can operate a 503A pharmacy and a separate 503B facility, and many do — the 503A serves patient-specific demand and the 503B serves clinics. What they need from a system is one platform with separate facilities, separate formulation sets where required, and one order model that handles prescription-driven and batch-driven work with the right rules for each. In Pharmacy Flow facilities are first-class with their own locations, capabilities and routing; the order lifecycle and lot lifecycle are enforced in the database for both; and reporting runs per facility or across the organisation. The platform overview describes the modules; security and compliance describes the enforcement.
Undecided between the two?
Bring your product list and your customer list. We will map them onto the rules for each section and show you what the platform enforces for both.
What each model demands from software
| Need | 503A | 503B |
|---|---|---|
| Prescription record with DEA refill limits and pharmacist verification | Essential | Needed for patient-specific work |
| Ship-to-state licence gate | Essential | Essential |
| Formulation versions with signed approval and change control | Important | Essential |
| Batch record: components consumed with quantities, finished lot, BUD capped at component expiry | Important | Essential |
| QC-gated release enforced in the database | Important | Essential |
| Environmental monitoring with derived action status | Sterile only | Essential for sterile |
| Deviations, CAPA, change control, document control | Important | Essential |
| Part 11 signatures with re-authentication; append-only audit | Important | Essential |
| Unit serialization, SSCC cartons, per-unit recall | Important | Essential |
| Partner portal and idempotent ordering API | Telehealth-fed pharmacies | Clinic and health-system customers |
Further reading: 21 CFR Part 11 for pharmacies, USP <800> checklist, serialization and DSCSA, how to start a compounding pharmacy, sterile compounding software, and the resources index.
Frequently asked questions
Can one pharmacy be both 503A and 503B?+
A registered outsourcing facility is a 503B and not a 503A at the same location and registration. One organisation can, and often does, operate a 503A pharmacy and a separate 503B facility. Software that treats facilities as first-class with their own rules is what makes that workable.
Does a 503B need a patient-specific prescription?+
No. A 503B may compound with or without a prescription and may distribute office stock to healthcare facilities and prescribers, labeled "Not for resale" and with the statement that it was not compounded for an identified patient.
Is a 503B subject to USP <797>?+
A 503B is subject to cGMP under 21 CFR 210/211 rather than exempt under USP; in practice FDA's cGMP guidance for outsourcing facilities and inspectors treat the USP chapters as a floor, and most 503Bs follow them and more.
Can a 503A ship nationwide?+
Only within the 5% interstate cap unless its home state has signed FDA's MOU, and only into states where it holds a nonresident pharmacy licence. Most states have signed the MOU; check yours.
Does a 503B have to be a pharmacy?+
Federally, no — but compounding must be by or under the direct supervision of a licensed pharmacist, and many states require a 503B to hold a state licence or registration in addition to FDA registration.
Which is cheaper to run?+
A 503A, by a wide margin, because it is exempt from cGMP and per-batch release testing. A 503B's facility qualification, quality unit and testing costs only make sense at volume on a narrow product set.
Where do GLP-1s fall?+
During the FDA-declared shortages, both 503As and 503Bs compounded semaglutide and tirzepatide under the shortage provisions. With the shortages resolved, the essentially-a-copy rules apply to each section, and the position continues to develop. Take current advice before compounding a GLP-1.
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