I'm certain it's aggregates, which is primarily a function of the excipients (or lack thereof) creating an environment that encourages aggregation.
The 30+ varieties of pharma rHGH are all using the same molecule. 99% of their work is ensuring it stays stable via the formulation.
Unfortunately excipients just aren't a focus of our community.
We could make a lot of progress by starting with one simple cheap test that doesn't even require a lab. Check the PH of the reconstituted solution on a PH strip.
I'll bet if we gather that data, we'll see a clear correlation between visible aggregates and PH.
All that's needed is someone to develop a standardized protocol, so we're all using the same test strip (from Amazon), put a drop on, and wait the same amount of time.
@readalot
That would be a start to figuring out whose formulations are getting it right.
PH is THE most critical element to peptide stability. The wrong PH can cause near instant degradation, and more over time.