ConsumerLab.com's answer explains
Our vitamin B12 injections are delivered by trained professionals in a calm, safe, and comfortable environment, tailored to your individual needs
The well-known geriatrician-haematologist Larry Solomon, working at Yale University in the USA, wrote 20 years ago: if I had treated only those people who actually had too low serum B12 and elevated MMA values, then I would not have treated approximately two-thirds of the people with a favourable response to B12 supplementation (note: partly via injections, partly via oral supplementation)
This product is not intended for human consumption, veterinary use, cosmetic use, diagnostic use, medical use, therapeutic use, supplementation, wellness use, performance enhancement, personal use, or administration to humans or animals
***12 mg requires 3 vials (15 mg total in 3.0 mL)