MikeFit_NJ said:

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

Pushing back on MikeFit_NJ 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.

PedsEndoPhilly said:

My pharmacy stopped supplying with three weeks notice and a letter that explained nothing, so I went and read the statute.

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 $147/month vs $1,237 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.

InsuranceTom said:

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

Price comparison for compounded supply across sources I've used:

I use the 503B option — best balance of quality, cost, and legality. The brand price is insane but insurance can help if you qualify.

Following on from MounjBrad — and this may be the naive question:

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.