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Background. Vitamin B₁₂ deficiency is common, increasing with age. Most people are treated in primary care with intramuscular vitamin B₁₂. Several studies have reported equal efficacy of oral administration of vitamin B₁₂.

Objectives. We set out to identify randomized controlled trial (RCT) evidence for the effectiveness of oral versus intramuscular vitamin B₁₂ to treat vitamin B₁₂ deficiency.

Methods. We conducted a systematic review searching databases for relevant RCTs. Outcomes included levels of serum vitamin B₁₂, total serum homocysteine and methylmalonic acid, haemoglobin and signs and symptoms of vitamin B₁₂ deficiency.

Results. Two RCTs comparing oral with intramuscular administration of vitamin B₁₂ met our inclusion criteria. The trials recruited a total of 108 participants and followed up 93 of these from 90 days to 4 months. In one of the studies, mean …