503A or 503B: which one should be filling your prescription

Compounding pharmacies in the United States fall into two categories under the Federal Food, Drug, and Cosmetic Act. The difference is not size or sophistication. It is what they are permitted to do.

503A: patient-specific

A 503A pharmacy compounds against a prescription for an identified individual patient. It is licensed and inspected by its state board of pharmacy, and it compounds to the USP chapters.

What it may not do is compound in advance for general distribution. Each preparation traces to a prescription for a named patient.

503B: outsourcing facilities

A 503B outsourcing facility registers with the FDA, complies with current Good Manufacturing Practice, and may compound in batches without patient-specific prescriptions — supplying office stock to clinics, for instance.

That capability comes with a heavier regulatory burden: FDA inspection, cGMP, and adverse event reporting obligations.

Which you need

If you are writing for a named patient, a 503A pharmacy is the correct route and the simpler one.

If you want preparations held in your office and administered to whoever presents, that is office stock, and it must come from a 503B facility. A 503A pharmacy cannot lawfully supply it, and a pharmacy that offers to is telling you something important about how it reads its own licence.

The question worth asking

"Which are you, and what is your licence number?" A straight answer takes ten seconds and tells you what a pharmacy may legally make for you. Both answers are good answers; the wrong one for your use case is the problem.