There are multiple medical conditions related to vitamin B12 deficiency
Int J Pept Res Ther 28:87 Veldhuizen EJ, Schneider VA, Agustiandari H, van Dijk A, Tjeerdsma-van Bokhoven JL, Bikker FJ, Haagsman HP (2014) Antimicrobial and immunomodulatory activities of PR-39 derived peptides
Niacin helps your digestive system, skin, and nerves function properly
10.26402/jpp.2018.3.11 5 Belosic HalleZ.VlainicJ.DrmicD.StrinicD.LueticK.SucicM.et al (2017)
Thats what makes it readily available via telehealth provider like AgelessRx, whereas peptides like Ipamorelin which were never FDA-approved lack that pathway and face greater regulatory restrictions
Its mechanism is purely metabolic: it directly targets lipid metabolism via inhibition of NNMT and restoration of cellular NAD+