A 2018 peer-reviewed review of the copper peptide GHK described an older 12-week study that compared a GHK cream against both of those ingredients on the thigh skin of women.
According to the review, the GHK cream improved collagen production in 70 percent of the women who used it, against 50 percent with the vitamin C cream and 40 percent with retinoic acid.
The original 1998 study was small and is known mainly through this review, written by the scientist who discovered GHK and whose company sells copper-peptide skincare. No large, independent, modern trial has repeated the three-way comparison, so the result stands as one small, old study rather than settled dermatology.
Read the original study
One small trial, still waiting for a larger one.
Source
- Pickart, L., & Margolina, A. (2018). Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data. International Journal of Molecular Sciences, 19(7). https://doi.org/10.3390/ijms19071987