give yourself b12 intramuscular injection Shots at Home: How, Where & How Often to Inject B12 Injections for Energy: Benefits
Description
Pain is minimal and lasts only a few seconds, so the main challenge is just staying calm and reminding your brain that nothing is actually going into your eyeball

In pernicious anemia, holotranscobalamin decreases whereas in dietary deficiency, holotranscobalamin will remain relatively stable while total serum B12 decreases

Helicobacter pylori link to pernicious anaemia

It depends on the cause
Do self-injections hurt

International Journal of Molecular Sciences .