Answering the narrow version, because the broad one does not have a single answer. Resolution therefore closed the doors unevenly, and the asymmetry follows from the bulks lists. For 503B the shortage clause was the only route to these molecules, so that route shut completely. A 503A pharmacy can still argue a doorway via "component of an approved drug" — but only for the substance in the form present in the approved product, which is exactly where the base-versus-salt argument lives, and it does nothing about the copy restriction, which came back into force on resolution.

NeuroNate said:

Resolution therefore closed the doors unevenly, and the asymmetry follows from the bulks lists.

Agreed, and the enforcement dates were staggered by category — 503A first, 503B a few weeks later — because outsourcing facilities have manufactured inventory and clinic contracts to unwind while a 503A makes to order.

CarlaRPh_TPA said:

Two pharmacies quoted me last year, one describing itself as 503A and one as 503B, and I assumed 503B just meant bigger until both stopped within…

Same position here, arrived at the long way round. The shortage clause is the answer to the second question and it is a subtraction rather than an addition. Both exemptions forbid compounding something that is essentially a copy of a commercially available approved product. A product FDA has listed as in shortage is not treated as commercially available, so listing removed the objection that otherwise blocked compounding. It never created a permission; it withdrew a prohibition, which is why it evaporated the moment the supply fact changed.

Adding the clinical framing, because it changes how the question reads.

Compounding pharmacy red flag checklist for compounded supply — if ANY of these apply, find a different source:

1. No verifiable physical address
2. No pharmacist available for consultation
3. COA not available or clearly template/fake
4. Prices dramatically below market ($30-40/month = suspicious)
5. No prescription required
6. Ships without cold pack or temperature control
7. No batch/lot numbers on product labeling
8. Pushes "research use only" products for human injection

Your health depends on product quality. Don't cut corners on source verification.