This one has a reasonably settled answer, so here it is. 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.

Dr.NutriCornell said:

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

No disagreement with Dr.NutriCornell. One condition attached. Worth adding the genuine exception, because it is real and narrow: a change made for an identified patient where the prescriber determines it produces a significant clinical difference for that patient. A grid of fixed doses offered to everybody is not that, whatever the intake form says.

Happy to go further on any of that.

KarenAZ_mom 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…

This matches mine closely enough to be worth saying so. 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.

From the other side of the consultation, briefly.

Regarding compounded supply compounding legality: compounding pharmacies can legally produce semaglutide and tirzepatide while these drugs remain on the FDA shortage list. If/when the shortage resolves, the legal landscape may change.

Stay informed. The FDA shortage list is updated regularly. Current status as of my last check: semaglutide partially resolved shortage, tirzepatide still in shortage. This directly impacts compounding availability.