Dr.KarenChen said:

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

Pushing back on Dr.KarenChen here. 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.

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…

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.

NurseKim_ATL 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.

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

What actually distinguishes 503A from 503B, in terms of what each may make and from what starting material?

OP back with an update, since a thread like this is useless without one.

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.