With intramuscular injections of B12, any excess will result in high levels within your blood so you may experience side effects such as headache, dizziness, tiredness, or gastrointestinal issues including nausea, until your body has metabolised any excess through your kidneys enroute to excretion via urine
Think: a tiny bit of redness, slight swelling, or tenderness where the needle went in
Methyl B12 supports energy, cognition, detoxification, and nervous system repair
Cyanocobalamin side effects: Consumer information
They are more likely to have stomach and digestive problems
Without enough B12, you can experience neurological issues like numbness, tingling, or balance problems