Though allergies to cobalt are rarely dangerous, taking any form of B12 supplement, whether by injection, tablet, or topically applied gel, may result in an uncomfortable, itchy rash
Pharmacokinetics: Cyanocobalamin is administered intranasally, orally, and parenterally, while hydroxocobalamin is administered only parenterally. Once absorbed, vitamin B12 is highly bound to transcobalamin II, a specific B-globulin carrier protein and is distributed and stored primarily in the liver as coenzyme B12. The bone marrow also stores a significant amount of the absorbed vitamin B12. This vitamin crosses the placenta and is distributed into breast milk. Enterohepatic recirculation conserves systemic stores. The half-life is about 6 days (400 days in the liver). Elimination is primarily through the bile; however, excess cyanocobalamin is excreted unchanged in the urine
Better Ways to Address B12 Deficiency The ideal and safest way to consume enough of any nutrient is getting it naturally through whole food sources
For instance, many peptides used in Longevity Research have vastly different pharmacokinetic profiles