The dose needed depends on how bad the deficiency is, your age, and your health
Dijk, W
They might be having a severe allergic reaction
Most patients experience minimal discomfort and can resume daily activities immediately after the appointment
Chapman LE, Darling AL, Brown JE (2015) The association between the biguanide drug metformin and vitamin B 12 deficiency in diabetic patients: a systematic review
In children aged 6 through 35 months who received FLUARIX QUADRIVALENT, the most common (10%) solicited local adverse reactions were pain (17%) and redness (13%), and the most common systemic adverse reactions were irritability (16%), loss of appetite (14%), and drowsiness (13%) The most common (10%) solicited local adverse reactions with FLULAVAL in adults were pain (51%), redness (13%), and swelling (11%), and the most common solicited systemic adverse reactions were fatigue (20%), headache (18%), and muscle aches/arthralgia (18%)