mike_nyc said:

They are not contradictory, they measure different things, and this is the single most common misreading of a certificate.

I am more sceptical of certificates as a category than this thread is. The document tells you about a sample somebody chose to send, at a moment in time, and nothing about the vial in your hand. Independent purchase-and-test is a different quality of evidence and everything else is inference.

Dr.PulmRoch said:

I have a certificate reporting 99.2% purity and 6.1mg content on a vial sold as 5mg, and I cannot work out whether those two numbers are consistent or…

Vendor quality matters when discussing certificates of analysis. I've tested my last 3 batches through Janoshik and purity has ranged from 97.4% to 99.0%. Consistency is key.

For anyone new: always request the COA, and consider independent verification. The $300 for a Janoshik test is worth the peace of mind.

labquiet_amy said:

I am more sceptical of certificates as a category than this thread is.

My vendor review relevant to certificates of analysis: ordered 5 times from my current compounder. Consistency has been excellent.

Shipping: Same-day local pickup
Packaging: Professional, discreet, proper labeling with lot/batch numbers
Purity: 98.2% average across orders (Janoshik verified)
Customer service: Responsive within 6 hours
Price: $130/month for tirzepatide 10mg equivalent

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

Why two laboratories report different purity for the same batch, and which number to believe?

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

Purity and content being different measurements was the piece I was missing. The vial was overfilled and pure, which is a very different problem from the one I thought I had.