mixing b12 with hcg injections Methylcobalamin | Vitamin How It Works? – HCG

Vitamin B12 injections are medically necessary for patients with pernicious anemia, severe malabsorption syndromes, post-bariatric surgery absorption failure, or critically low B12 levels with neurological symptoms

2) Headaches Headaches are frequently described during early use

Froesch ER, Brgi WA, Ramseier EB, Bally P, Labhart A

Published research has proposed and examined several potential mechanisms: Beta-3 Adrenergic Receptor Interactions A substantial body of published research has examined interactions between this GH fragment and beta-3 adrenergic receptors (3-AR) in adipose tissue research models

Conclusion To answer the original question directly: high B12 levels themselves don't typically cause symptoms