Posting my experience because I couldn't find much online that matched what I had, and the only pages that came up were vendor sites describing something different.

Stats: 2 injections total, 1 mg each, subcutaneous. Product came with a clean third-party COA (HPLC purity \~99.9%, ICP-MS heavy metals not detected, sterility by PCR, low endotoxin). So I don't think this was a contamination or bad-vial issue.

What happened: every site developed a reaction that started a few hours after injection, peaked around the 24 hour mark, and fully resolved within about 48 hours with no residual lump or mark. Well-defined oval patch of redness, a few cm, flat to very slightly raised. Same pattern across all four sites. No stinging in the first minutes, no immediate wheal, no facial flushing, no systemic symptoms.

What I've figured out so far: the timing (onset over hours, peak at 24h) doesn't fit the histamine/mast cell reaction most vendor pages describe, which resolves in minutes to an hour or two. A delayed peak like that is more consistent with either late-phase local inflammation from the copper itself, or a delayed-type (cell-mediated) hypersensitivity.

I've stopped. Not planning to push through it, since sensitization only consolidates with repeated exposure. 

Questions for the group:  
\- Anyone else get a DELAYED reaction like this rather than the immediate sting? Most reports I see are the immediate kind.  
\- If you patch tested after something similar, what did it show?  
\- Did yours change across doses (faster/bigger each time) or stay consistent?

Not medical advice, just documenting in case it helps someone searching later.

Delayed injection site reaction to subcutaneous GHK-Cu (peaks ~24h, resolves ~48h) — anyone else?