Levels in the low-normal range, between 200 and 300, may warrant supplementation even without overt symptoms, particularly in patients with risk factors for deficiency
Many notice a lift within a few days
Neelakantan H, Vance V, Wetzel MD, Wang HY, McHardy SF, Finnerty CC, Hommel JD, Watowich SJ. Selective and membrane-permeable small molecule inhibitors of nicotinamide N-methyltransferase reverse high-fat diet-induced obesity in mice. Biochem Pharmacol. 2018 Jul;154:161-171. doi: 10.1016/j.bcp.2018.05.003. Epub 2018 May 5. PMID: 29738706; PMCID: PMC6015571
B12 injections deliver vitamin B12 directly into the bloodstream, avoiding the digestive system where absorption can fail
After that, they need a shot every month