Are there any GHK-Cu side effects
systemic adverse events are rare in preliminary reports
Not "I'm a bit tired" fatigue

Protein S -nitrosylation, the covalent attachment of nitric oxide (NO) moiety to the reactive thiol group of a cysteine residue to form S -nitrosothiol is an important PTM for most classes of proteins ( S -nitrosylated proteins such as Bcl-2, p53, HIF-1, PTEN, and Src are involved in cell survival, angiogenesis, tumorigenesis, and response to cancer treatment ( S -nitrosylation of Bcl-2, which inhibits its ubiquitination and subsequent proteasomal degradation ( S -nitrosylation on Cys498 residue of Src kinase induces autophosphorylation, which promotes nitric oxide-mediated cell invasion and resistance to anoikis in cancer cells ( S -nitrosoglutathione promote S -nitrosylation at the Cys183 residue of extracellular signal-regulated kinase 1/2 (ERK1/2), which leads to inducing apoptosis in U251 glioma cells ( S -nitrosylation affects a variety of proteins that play important roles in the cellular dysfunctions and contribute to cancer progression and response to chemotherapy

The clinical literature on glutathione spans skin brightening, liver protection, oxidative stress reduction, and immune modulation