Importantly, GHK-Cu is also highly synergistic with other treatments
Arnold HH, Heinze H (1990)
It is one of the more promising natural preservatives that can be used even alone (recommended at 2-4%), but it's not as effective as more common alternatives, like parabens or phenoxyethanol.
Food had no effect on the extent of exposure (AUC) of the cetirizine tablet or chewable tablet, but Tmax was delayed by 1.7 hours and 2.8 hours respectively, and Cmax was decreased by 23% and 37%, respectively in the presence of food
A more dilute solution may be easier to measure accurately for small doses, while a more concentrated solution may be preferred if larger doses are needed
Doctors may prescribe it off-label to treat obesity