My experience is they deliver faster than they promise
Strict vegetarians and women planning to become pregnant should take a multivitamin supplement daily or eat fortified cereal, which would ensure a daily intake of 6 to 30 g of vitamin B 12 in a form that is easily absorbed
30638692 Park EG, Lee J, Lee J
This 1,000 mcg initial loading dose protocol quickly fills up vitamin B12 stores
A significant sign that the injections are working is a reduction in symptoms of vitamin B12 deficiency, such as weakness, rapid heart rate, easy bruising or bleeding, and pale skin
B12 injections may help lower levels of homocysteine, an amino acid that, when elevated, can be a risk factor for heart disease and stroke