GHK-Cu downregulates acute-phase and pro-inflammatory cytokines (TNF-?, IL-6), upregulates anti-oxidant defenses (including superoxide dismutase, Nrf2 and HO-1 pathways), and suppresses fibrotic signaling by inhibiting TGF-?1/Smad2/3 activation
Using them can lead to failed tests and suspensions

Sources & references BioMed Research International GHK Peptide as a Natural Modulator of Multiple Cellular Pathways in Skin Regeneration Pickart L, Vasquez-Soltero JM, Margolina A 2015 DOI: 10.1155/2015/648108 PMID: 26236730 Read on PubMed Oxidative Medicine and Cellular Longevity The human tripeptide GHK-Cu in prevention of oxidative stress and degenerative conditions of aging Pickart L, Vasquez-Soltero JM, Margolina A 2012 DOI: 10.1155/2012/324832 PMID: 22666519 Read on PubMed Journal of Biomaterials Science, Polymer Edition The human tri-peptide GHK and tissue remodeling Pickart L 2008 DOI: 10.1163/156856208784909435 PMID: 18644225 Read on PubMed Brain Sciences The Effect of the Human Peptide GHK on Gene Expression Relevant to Nervous System Function and Cognitive Decline Pickart L, Vasquez-Soltero JM, Margolina A 2017 DOI: 10.3390/brainsci7020020 PMID: 28212278 Read on PubMed FEBS Letters Stimulation of collagen synthesis in fibroblast cultures by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+ Maquart FX, Pickart L, Laurent M, et al

Despite claims you may have read, GHK-Cu has not been shown in peer-reviewed research to inhibit 5-alpha reductase or reduce DHT in human tissue
Injectable administration often shows results faster than topical
The latter is far more readily available online but far less safe