I have mixed collagen peptides into my protein shakes for more than a year and have been using GHK-CU for the past three months. I had planned to drop the collagen because the cost did not seem justified by the results, yet the two appear to work together now that GHK is in the picture. Results might improve further if I could raise my overall protein intake, something I have always found difficult.
Evidence on collagen supplements has been mixed for years. Still, when using GHK-cu or BPC157 to repair tendons or improve skin, it makes sense to supply the raw materials the body needs for that work. Some argue that enough total protein removes the need for extra collagen, yet high methionine from meat can lower available glycine, and glycine forms about a third of collagen. Studies have found higher glycine in vegans than in heavy meat eaters. So if the aim is better skin, tendons or hair, adding collagen gives the body what it needs to carry out the repairs.