inject slow — if it burns you're in muscle, not fat, or ph is off. let the vial warm to room temp. i pinch hard so the poke feels less. with one peptide i get itchy at the site, not sure if that's normal yet.
For topical use, GHK-Cu concentration and carrier matter as much as source. At $69 per 100mg, the per-use cost is low for homemade serums. Purity can vary across vendors at similar price points, so checking testing data helps.