are there any side effects from having b12 injections Shot Guide: Benefits, Dosage & What Are B12 Shots? 5
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Those with gout, polycythemia vera, or specific vitamin deficiencies (particularly folic acid and iron) should undergo thorough medical evaluation [13]

Treating vitamin b12 deficiency or folic acid deficiency anaemia : Most cases of vitamin B12 and folate deficiency can be easily treated with injections or tablets to replace the missing vitamins

Double-check dosages: Always confirm the amount of B12 and expiration dates on vials
1 2 3 Wintrobe's Clinical Hematology Thirteenth Edition

It makes sure the benefits of the first treatment last longer