HPLC_Greg said:

The shortage clause is the answer to the second question and it is a subtraction rather than an addition.

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. A research-chemical supplier selling lyophilised powder labelled research use only is not compounding and is not claiming to. It is a different legal universe with no pharmacy oversight, no patient relationship and no content guarantee, and conflating the two in these threads helps nobody.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

PurityPaulOR 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…

Compounded has been just as effective for me. If compounded supply is the concern, the COA from my 503B pharmacy shows 99.1% purity. Verified by Janoshik.

amsterdam_pete said:

A research-chemical supplier selling lyophilised powder labelled research use only is not compounding and is not claiming to.

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 still in shortage, tirzepatide removed from shortage list. This directly impacts compounding availability.

A narrower follow-up, since the general answer is now clear:

Why a shortage listing created a legal pathway at all, since a shortage is a supply fact rather than a permission?

Closing the loop on my own question.

The bulks-list asymmetry was the piece I had missed entirely. It explains why one of my two pharmacies is still arguing it can supply and the other simply stopped.