The authors themselves highlighted substantial heterogeneity between products, sequences, doses, outcome measures and study quality
Among them are the following: A thirty-five-year-old man who starts wetting himself, and who can no longer walk steadily or grip with his hands

The pharmacological profile of GHK-Cu observed in preclinical models covers a broad spectrum of activity: Stimulation of extracellular matrix synthesis influence on the production of collagen, elastin and glycosaminoglycans in dermal fibroblasts Pro-regenerative and pro-angiogenic effects in in vivo and in vitro wound healing models Modulation of gene expression in transcriptomic studies, the impact on hundreds of tissue repair and antioxidant defense genes Transport of copper ions GHK as a physiological carrier of Cu, a cofactor of matrix enzymes Antioxidant and anti-inflammatory activity reduction of oxidative stress markers in cell models GHK-Cu is a model ligand for testing in the group of plasma peptides connective tissue remodeling and copper biology combines a signaling function with trace element transport, making it a tool for studying the interface between copper metabolism and extracellular matrix repair

GSH levels affect weight loss in individuals with metabolic syndrome and obesity following dietary therapy Chen J., et al
This is the most significant limitation No statistical significance testing: The paper does not report p-values or statistical tests