Choosing the Right Needle and Syringe for B12 Injections: A Complete Guide Methylcobalamin Injection (Vitamin B12) Empower Pharmacy Vitamin B12 is something that all women are always deficient of. Taking injections is the best solution to it but it can give you a reaction., Initially it is very itchy and painful but it gets better Vitamin B12 Side Effects, What They Mean and More Dr. Axe Experiencing itchy, red welts after your peptide injections? You're not alone, and the peptide itself usually isn't the problem. The real culprits? Histamine release, mast cell activation, gut imbalances, hormonal shifts, or Common & Rare Side Effects of Vitamin B12 Injections