I have found a b12 100mg bottle for sale on a vet website pretty cheap. Here is the breakdown of the ingredients in this vet b12:
Each mL contains:
Cyanocobalamin (B12) 1,000 mcg
Sodium chloride 0.22% w/v
Ammonium sulfate 0.1% w/v
Citric acid 0.01% w/v
Sodium citrate 0.008% w/v
Benzyl alcohol (preservative) 1.0% v/v
Is this okay for human use?