6 micrograms b12/day. To replace deficiencies, im shots bypass gut absorption problems that can contribute to deficiency in the first place. 1, 000 micrograms of intramuscular cobalamin can be given once/day for 10 days, then once/week for four weeks, followed by once/month for life. Sublingual b12, 500-1000mcg/day. The form of B12 (cobalamin) may be important; see comment.