503A and 503B give compounders different jobs

503A and 503B sound like filing labels. They’re sections of the Federal Food, Drug, and Cosmetic Act, and they help explain who is responsible for a compounded medicine.

Compounding means making or changing a medicine for a medical need. FDA’s compounding explanation makes a key distinction: a compounded drug is not FDA-approved. Neither number changes that.

FDA’s prescription guidance covers this framework. A licensed pharmacist in a state-licensed pharmacy or federal facility, or a licensed physician, can compound when the legal conditions are met.

Limited preparation ahead of expected prescriptions is allowed. But the full guidance requires a valid patient-specific prescription before distribution. That means a prescription for an identified person, rather than a general plan to supply a group.

The useful question for your care is why this preparation fits your needs. An old shortage announcement can’t answer that for you.

An outsourcing facility compounds sterile (germ-free) medicines in batches and chooses to register with FDA. It need not be a licensed pharmacy or obtain individual prescriptions. It must follow federal manufacturing rules, inspections and reporting requirements.

FDA’s registration explanation is clear: registration alone proves neither compliance nor drug approval. “Registered” is one piece of information, not a quality verdict.

State boards generally oversee ordinary pharmacies day to day; FDA primarily oversees outsourcing facilities. The two frameworks assign different duties rather than a simple better-or-worse ranking.

FDA’s 1 April 2026 update said neither semaglutide nor tirzepatide was on the shortage list or the 503B bulks list of allowed raw ingredients. So 503B facilities couldn’t compound them from those raw ingredients.

Under 503A, a pharmacist or physician can’t make what is essentially a copy of a commercially available drug regularly or in excessive amounts. A changed preparation falls outside that copy definition when the prescriber determines and documents that the change makes a significant difference for the named patient. The other legal conditions still apply.

Safety matters under either section. FDA warns that contamination or the wrong amount of active ingredient can cause serious harm. A supply problem doesn’t make those risks smaller.