The difference is the preservative
CAN I TAKE A B12 SUPPLEMENT INSTEAD OF AN INJECTION
At 12mg weekly using 20mg vials reconstituted with 1mL (20mg/mL), each dose requires 60 units, and each vial provides approximately 1.7 weekly doses

A physician investigating unexplained hypercobalaminemia will typically order some combination of the following: Complete blood count (CBC) with differential to check for abnormal red blood cell, white blood cell, or platelet counts Liver function tests (ALT, AST, ALP, bilirubin, albumin) to assess liver health Kidney function tests (creatinine, BUN, estimated GFR) to evaluate renal clearance Peripheral blood smear if a myeloproliferative disorder is suspected Abdominal imaging (ultrasound or CT) if liver or abdominal pathology is a concern Cancer-specific markers or screenings if clinical suspicion warrants them The NIH Office of Dietary Supplements fact sheet notes that observational data from a Danish registry analysis of 757,185 people found the adjusted 1-year cancer risk was 1.74 to 4.72 times higher among those with B12 above 813 pg/mL compared to those in the normal range of 203 to 813 pg/mL

When the FDA places a peptide in a restricted or high-risk category [known as Category 2], it is explicitly signaling that it has identified safety concerns and that enforcement discretion does not apply. But, as Hajduczok notes, just because something is not FDA-approved doesnt mean its illegal to compound, but the restricted peptides should not be compounded
The natural sources are all animal-derived: meat, fish, eggs, milk and cheese