How much vitamin B12 should you take if you already have a deficiency?

Individuals suffering from vitamin B12 deficiency should take 500 micrograms of cyanocobalamin sublingually, 1,000 micrograms of intramuscular cyanocobalamin daily or 125 to 2,000 micrograms of cyanocobalamin by mouth, advises Mayo Clinic. People who are deficient due to proton pump inhibitor therapy should use cyanocobalamin nose sprays daily.

Vitamin B12 is safe even at high doses, and there is no known limit for safe consumption, according to WebMD. The recommended daily allowance of vitamin B12 for people age 14 and older is 2.4 micrograms a day. People over age 50 are more likely to be deficient in vitamin B12, causing fatigue, memory loss and weakness.