This uncertainty is recognised in laboratory medicine guidance from bodies such as the Association for Clinical Biochemistry and Laboratory Medicine (ACB) and the Royal College of Pathologists (RCPath)
Values summarised from cited preclinical studies (see references below)
The wellness positioning of B12 shots as an energy or weight-loss boost for healthy people is not supported by the NHS, by NICE, or by published trial evidence
Duzel A, Vlainic J, Antunovic M, Malekinusic D, Vrdoljak B, Samara M, et al
No, but you can react negatively to other ingredients in supplements
The original Durham Peptides packaging provides adequate light protection