Drug-Drug Interactions: Key B12 PFS 1500 mcg Injection 1 ml may interact with anticancer medications (arsenic trioxide), antimetabolites (mercaptopurine), antibiotics (chloramphenicol), and oral contraceptives
On the other hand, a single dose of 600mg reduces the need for multiple doses
"Retatrutide, a GIP, GLP-1, and glucagon receptor agonist for obesity: A phase 2 trial." New England Journal of Medicine , 389(6), 514-526
If your skin doesnt seem to be getting through the adjustment period, you may need to stop using the product and seek out alternatives
Biochem Biophys Acta 1853:15131527 Qi W, Li J, Chain CY, Pasquevich GA, Pasquevich AF, Cowan JA (2013) Glutathione-complexed iron-sulfur clusters