The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.
Adults (18 years and older)
Recommended dietary allowances (RDAs) are 2.4 micrograms daily for adults and adolescents aged 14 years and older, 2.6 micrograms daily for adult and adolescent pregnant females, and 2.8 micrograms daily for adult and adolescent lactating females. Because 10-30% of older people do not absorb food-bound vitamin B12 efficiently, those over 50 years of age should meet the RDA by eating foods fortified with B12 or by taking a vitamin B12 supplement. Supplementation of 25-100 micrograms daily has been used to maintain vitamin B12 levels in older people. A doctor and pharmacist should be consulted for use in other indications.
For vitamin B12 deficiency, 125-2,000 micrograms of cyanocobalamin has been taken by mouth daily for up to 2.5 years or longer. Five hundred micrograms of sublingual (under the tongue) vitamin B12 has been used daily for up to four weeks. The following doses have been given intravenously (through the veins): 1,000 micrograms of intramuscular cobalamin once daily for 10 days (after 10 days, the dose was changed to once per week for four weeks, followed by once per month for life); 1,000 micrograms of intramuscular cyanocobalamin given on days 1, 3, 7, 10, 14, 21, 30, 60, and 90 of treatment. For vitamin B12 deficiency caused by long-term PPI therapy, cyanocobalamin nasal spray has been used for eight weeks. The exact dosage is unclear. One clinical trial tested patients' acceptance of intranasal vitamin B12 replacement therapy (500 micrograms per week).
To lower homocysteine levels, 60-400 micrograms of vitamin B12 has been taken by mouth daily, as part of a B vitamin combination used for up to four years.
For prevention of anemia, the following doses have been taken by mouth: 2-10 micrograms of vitamin B12 daily combined with iron and/or folic acid for up to 16 weeks; 100 micrograms of vitamin B12 every other week plus daily folic acid and/or iron for up to 12 weeks.
For cognitive function, the following doses have been taken by mouth: 10 micrograms or 50 micrograms of cyanocobalamin daily for one month; and one milligram of cyanocobalamin weekly for four weeks. One 1,000 microgram vitamin B12 injection has been used daily for five days, followed by one 1,000 microgram injection monthly for five months.
For acute cyanide poisoning, an intravenous infusion of five grams of hydroxocobalamin (up to 20 grams) has been used.
For depression, one milligram of cyanocobalamin, through intramuscular injections, was used weekly for four weeks.
For hereditary sideroblastic anemia, 100 micrograms of intramuscular vitamin B12 has been used monthly, with or without daily folic acid, for up to four months.
Children (under 18 years old)
Recommended dietary allowances (RDAs) have not been established for all pediatric age groups; therefore, adequate intake (AI) levels have been used instead. The RDAs and AI levels of vitamin B12 are as follows: for infants 0-6 months old, 0.4 micrograms (AI); for infants 7-12 months old, 0.5 micrograms (AI); for children 1-3 years old, 0.9 micrograms; for children 4-8 years old, 1.2 micrograms; and for children 9-13 years old, 1.8 micrograms.