how to give a b12 injection to yourself self sites B12 Injections at Home · PA Relief Ivy Grove Surgery : Self-administration
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Do You Rub After an IM Injection

Interestingly, treating mice with the salvage precursor NR resulted in NAD + repletion in muscle stem cells (MuSCs) of young and aged mice 108

Its also not recommended for older adults
Risk factors that should prompt consideration of B12 deficiency include advancing age (reduced stomach acid production), strict vegan or vegetarian diets, pernicious anaemia, gastrointestinal surgery (particularly gastric bypass or ileal resection), long-term use of certain medications (metformin, proton pump inhibitors, H2-receptor antagonists), nitrous oxide exposure (including recreational use), and conditions affecting the gut such as Crohn's disease or coeliac disease