hannah_MT said:

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

Compounded has been just as effective for me. If compounded supply is the concern, the COA from my 503B pharmacy shows 99.1% purity. Verified by Janoshik.

One thing that is still open after Dr.LipidDallas’s answer:

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

Dr.NateNeph said:

Compounded has been just as effective for me.

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.

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.

TinaHashiRN said:

Compounding pharmacy red flag checklist for compounded supply — if ANY of these apply, find a different source: No verifiable physical address No…

That is correct as far as it goes, and here is where it stops going. Worth adding the genuine exception, because it is real and narrow: a change made for an identified patient where the prescriber determines it produces a significant clinical difference for that patient. A grid of fixed doses offered to everybody is not that, whatever the intake form says.

Ask again with the specifics and you will get a better answer than this one.