GHK-Cu side effects and what's normal

The most common thing patients report with GHK-Cu is a sting when they inject. It is expected, and there are things that help.

Common and usually temporary

Stinging or burning during and just after the injection. GHK-Cu is more acidic than the other peptides, and that is what causes it. It does not mean your vial is bad or that you are allergic. See "How do I store, handle, and inject GHK-Cu?" for the five things that help.
Redness, itching, or a small lump where you injected. Common with any peptide. Rotating sites is the fix.
A welt, redness or burning at the spot that is still there a day or two later. This is common with GHK-Cu and fades on its own over a few days. It is not a sign that something is wrong.

An allergic reaction, as with any peptide. This is rare.

A side effect is severe, persistent, or getting worse instead of better. At the injection site, that means a welt or redness that is growing, spreading or warm to the touch, or one that is not fading after 3 days
The sting is bad enough that you are considering stopping: there is a protocol for it and we would rather help you than lose you
Anything feels wrong enough that you are unsure about your next dose
You notice signs of an allergic reaction such as a rash, hives, or swelling. For trouble breathing or swelling of the face, lips or tongue, seek emergency care first, then let us know. This is different from the expected sting.