The common approach is alternating nights: tretinoin on its own evenings and GHK-Cu on the nights between, which gives skin recovery support without a tolerance or pH clash
For a provider-focused clinical profile of this peptide mechanism, protocols, and safety see Empires GHK-Cu clinical reference guide
It does not claim lifespan extension has been proven
Propionyl-L-carnitine in intermittent claudication: double-blind, placebo-controlled, dose titration, multicenter study
doi: 10.14310/horm.2002.11165
For example, a study found that rotenone-induced microbiota dysbiosis is implicated in the pathogenesis of Parkinsons disease via the microbiota-gut-brain axis, and fecal microbiota transplant (FMT) alleviates systemic inflammation, intestinal inflammation, and barrier destruction, attenuating BBB impairment and neuroinflammation