PurityPaulOR said:

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

This is where I part company with the consensus forming above. 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.

alex_tucson 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…

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.

NeuroNate said:

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

Compounding pharmacy customer here with experience relevant to compounded supply.

I've ordered from 4 different compounding pharmacies over the past 14 months. 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 8 orders. I pay $139/month vs $1,389 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.

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?

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.