I use topical GHK-Cu on my face, but for hair, you probably want AHK-Cu.
I mix The Ordinary multi-peptide hair serum (about 6ml) with 1g of raw AHK-Cu, giving me a concentration of around 1.6%. I use it nightly. Once a week, I also do a session with a straight AHK-Cu serum (lyophilized AHK-Cu...