I'm not seeing any links to credible research. But definitely skepticism. For example "Cinnamaldehyde_45" on Reddit:
This myth needs to die. Given the amount of skepticism I've seen on this subreddit every other time this topic has been brought up, I would have expected someone else to kill it by now. But since nobody has, I suppose I'll do the honors.
GHK-Cu is not a 5-ar inhibitor. As far as I can tell, this notion was confabulated by a few articles that concluded that since finasteride and GHK-Cu can both reverse hair loss, they must operate via the same mechanism, which is scientifically untenable.
Finasteride is a steroid. Specifically, an azasteroid, with an amidated (lactamated?) A ring. The only other difference between finasteride and testosterone is the substitution of the beta hydroxyl group on carbon 17 with a beta tert-butylamide substituent. Because of its similar structure, finasteride can bind to the active domain of 5-ar, inhibiting testosterone in the process. GHK can't do this because it's not a steroid—it's a peptide, and a fairly hydrophilic one at that (as demonstrated by its high affinity for Cu2+ ions). So, I wouldn't expect to find it anywhere near heavily-reduced steroids like testosterone and DHT (the latter being fully-reduced) in the cytosol. And I definitely don't see how it could inhibit enzymes with lipid/sterol-based substrates.
GHK is also known to operate via numerous anti-fibrotic mechanisms such as decreasing activation of cytokines like TGF-β, which shuts off the anagen phase of the hair cycle.
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