Melanotan II is the one getting the most attention, but any peptide marketed for cosmetic tanning falls into the same category: unapproved, unregulated, and untested for long-term safety in healthy skin
doi: 10.1007/978-1-4939-7407-8_19
Body composition assessment requires different tools: DEXA scans, bioelectrical impedance, or at minimum, waist circumference measurements
7,9 However, as shown in Supplementary Figure, a couple of compounds with free thiol group and disulfide bond are present in the low-molecular-weight fraction of rat plasma, which can react with Ellmans reagent and provide apparent values for glutathione and its disulfide
How much actually gets through the skin depends on the carrier, the formulation, the user, and even the weather
Unless you have specific reasons to try alternatives, GHK-Cu remains the standard