The distinction worth making before you start: these aren’t two doses of the same intervention, they’re two different use cases with pretty different evidence behind them. Topical GHK-Cu has decent wound healing and skin remodeling data, mostly from wound contexts but with some cosmetic work too. The proposed mechanism, copper ion release and downstream TGF-b/MMP signaling, is at least plausible and somewhat documented in vitro and in small human trials. Systemic subq is a different story. The longevity-adjacent claims, epigenetic reset, systemic stem cell signaling, come mostly from older rat studies and Pickart’s own research. I’m not dismissing it outright, but the human evidence is thin and the dosing rationale is largely extrapolated from animal work. If you’re 21 and the goal is skin, topical is where the actual signal lives. Subq at that age for longevity purposes is running on a mechanism story without much human data to verify against. Either way, pre-specifying what you expect to change and on what timeline matters before you start. Otherwise you’re just waiting and hoping, which makes it impossible to know if anything worked.