TirzTom said:

They are two different exemptions from the same federal requirements and they buy different things.

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.

nick_SD_fit 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 customer here with experience relevant to compounded supply.

I've ordered from 3 different compounding pharmacies over the past year. The quality variation is real — purity ranged from 94% to 101% of label claim based on independent Janoshik testing.

My current compounder (a 503B facility) has been consistently 98-101% purity across 6 orders. I pay $166/month vs $1,376 for brand. The savings are substantial and the product is equivalent in my experience.

Re: compounded supply — this applies whether you're using brand or compounded. The clinical principles are the same.

labquiet_amy said:

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

Compounding pharmacy response time test for compounded supply: I email customer service at odd hours to test responsiveness. A pharmacy that can't answer questions promptly is a red flag.

My current pharmacy: average response time 4 hours. They answered my questions about reconstitution thoroughly and professionally.

Communication quality is a proxy for operational quality. A pharmacy that communicates well is likely manufacturing well too.

One thing that is still open after tom_AK’s answer:

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

Reporting back.

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.