TirzTom said:

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

I read this differently from TirzTom, on substance rather than tone. 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.

Dr.PathRoch 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…

Compounding pharmacy licensing verification for compounded supply: before ordering, verify your pharmacy's credentials:

1. State Board of Pharmacy license — check on your state BOP website
2. FDA registration (for 503B) — check on fda.gov
3. DEA registration if handling controlled substances
4. PCAB accreditation — voluntary but demonstrates commitment to quality
5. USP <797>/<800> compliance for sterile compounding

This takes 10 minutes of research and could save you from receiving substandard or unsafe medication.

DataDave said:

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

503A vs 503B compounding pharmacies for compounded supply — this distinction matters enormously:

I strongly recommend 503B facilities. The FDA oversight and cGMP requirements mean more consistent product quality.

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.